So how does the Dolphin fit? Well it's size gives it a volume of 9,481.5m³, so it is between the Adder and Cobra Mk 3 on a small landing pad.

UPDATE: 28th June - twenty seven mega-ships now discovered

I have now visited twenty of the documented mega-ships. I will continue to visit the remaining ships as game-time allows. If you hear of any I've missed, please post the details in the comments.

Also, CMD Sektion has created a list of transcripts for all the discovered Generation Ships datalink logs, so if you don't want to fly there but still want to hear the generation ship's stories, view the uplink logs here. I'd recommend visiting the ships though, as seeing the huge derelict ships with the voices of long dead ghosts coming from the audio logs are something no transcript or screenshot can convey.

What are Mega Ships?

The mega-ships are huge, station-size ships that float or fly in deep space. While they have existed in Elite lore for some time they were only added into the Elite:Dangerous game at the 2.3 "Guardians" update.
They come in nine types; Tanker, Cargo, Asteroid Miner, Flight Operations, Prison Ship, Science Vessel, Passenger, Dredger and Generation Ship and those that have been found (so far) are all over populated space and out into deep space. So far nobody has seen a Dredger....
The flight operations type are dock-able (you can land a ship on them) and generally have small and medium pads. As my exploration ship is an Anaconda, I haven't landed on any as yet.
The generation ships were colony ships, launched from the centre of the bubble centuries ago before the FrameShift drive was invented, the crew intended for their children or grandchildren to be the colonists on distant worlds. There were thousands launched, but only a handful have so far been discovered. Those found all appear to be the ones that the colonists died and the mission failed. Those that succeeded may well have founded human colonies we have yet to discover.

Generation Ship Atlas

System: Charick Drift
Ship type: Bulk cruiser
Dockable: No
Location: 3.4Ls from main star. There are five ship log uplink nodes, which you can scan with a datalink scanner from 200m away. These reveal audio logs titled "no brakes" which tell of the crew's fate.
Distance from Sol: 28.6 ly

Naphtha Class Tanker

System: Okinura
Ship type: Tanker
Dockable: Yes
Location: 318Ls from main star
Distance from Sol: 32.5 ly

Hercules Class Bulk Cargo

System: Oduduro
Ship type: Cargo
Dockable: Yes
Location: 854Ls from main star
Distance from Sol: 40.11 ly

Alcatraz Class Prison

System: Milscothach
Ship type: Prison
Dockable: No
Location: 1,385Ls from main star in orbit around Milscothach 1A
Distance from Sol: 42.68 ly

Generation Ship Lycaon

System: Alaunus
Ship type: Bulk cruiser
Dockable: No
Location: Fly from main star to Alaunus 10, then set destination to the Horae system, but stay in supercruise in Alaunus and fly a further 22,000Ls away from Alaunus 10 until you see the generation ship POI on your contacts. There are five ship log uplink nodes, which you can scan with a datalink scanner from 200m away. These reveal audio logs titled "contagion" which tell of the crew's fate.
Distance from Sol: 52.62 ly

Generation Ship Thetis

System: Nefertem
Ship type: Bulk cruiser
Dockable: No
Location: fly 1,934Ls from main star to Nefertem 6A. There are five ship log uplink nodes, which you can scan with a datalink scanner from 200m away. These reveal audio logs titled "madness and ghosts" which tell of the crew's fate.
Distance from Sol: 53.46 ly

Lowell Class Science Vessel

System: Wolf 485A
Ship type: Science vessel
Dockable: No
Location: 9.67Ls from main star
Distance from Sol: 58.75 ly

The Midas

System: Zeus
Ship type: Flight operations
Dockable: Yes
Location: 7.89Ls from main star in orbit around Zeus 1.
Distance from Sol: 62.53 ly

Generation Ship Venusian

System: Kitae
Ship type: Bulk cruiser
Dockable: No
Location: Fly from main star with destination to the Zephyrus system, staying in supercruise in the Kitae system and fly a further 2,500Ls until you see the generation ship POI on your contacts. There are four ship log uplink nodes, which you can scan with a datalink scanner from 200m away. These reveal audio logs titled "boarding party" which tell of the crew's fate.
Distance from Sol: 63.12 ly

Fisher's Rest

System: Aldebaran
Ship type: Flight operations 
Dockable: Yes
Location: 2,513Ls from main star
Distance from Sol: 66.65 ly

Aquarius Class Tanker

System: Maya
Ship type: Tanker
Dockable: No
Location: the tanker is in orbit around Maya 5 an earth-like world with an ice ring, 530Ls from the main star.
Distance from Sol: 72.57 ly

Collinson Class Asteroid Ship

System: Gateway
Ship type: Asteroid miner
Dockable: No
Location: 299Ls from main star
Distance from Sol: 78.62 ly

Bowman Class Science Vessel

System: Asgaa
Ship type: Bulk Cruiser
Dockable: No
Location: 11.9Ls from main star
Distance from Sol: 90.05 ly

Bellmarsh Class Prison

System: Pohnpet
Ship type: Prison
Dockable: No
Location: 242Ls from main star orbiting Pohnpet 2A
Distance from Sol: 92.04 ly

Riker Class Prison Ship

System: Imiutli
Ship type: Prison
Dockable: No
Location: 1.72Ls from main star
Distance from Sol: 95.71 ly

The Harmony

System: Yum Kamcabi
Ship type: Flight operations
Dockable: Yes
Location: 1,235Ls from main star
Distance from Sol: 104.99 ly

Generation Ship Hyperion

System: Lalande 2966
Ship type: Bulk cruiser
Dockable: No
Location: fly 2,300Ls from main star to Lalande 2966 4, then set course toward the Yemaki system and fly a further 7,300Ls until you see the generation ship POI on your contacts. There are five ship log uplink nodes, which you can scan with a datalink scanner from 200m away. These reveal audio logs titled "the promised land" which tell of the crew's fate.
Distance from Sol: 121.53 ly

Generation Ship Odysseus

System: Ross 859
Ship type: Bulk cruiser
Dockable: No
Location: Fly from main star to the secondary star which is 52,000Ls away, when you reach the secondary star target Ross 859 B 1, you should then see the generation ship POI on your contacts. There are five ship log uplink nodes, which you can scan with a datalink scanner from 200m away. These reveal audio logs titled "our new eden" which tell of the crew's fate.
Distance from Sol: 165.98 ly

Generation Ship Pleione

System: Hez Ur
Ship type: Bulk cruiser
Dockable: No
Location: Fly from main star to the fifth planet in the system, when you reach Hez Ur 5 target the Teuten star system for a heading and fly a further 8,403Ls in super-cruise and you should then see the generation ship POI on your contacts. There are four ship log uplink nodes, which you can scan with a datalink scanner from 200m away. These reveal audio logs titled "the chromosome incident" which tell of the crew's fate.
Distance from Sol: 174.01 ly

The Gnosis ^{_{(pronounced "no sis")}}

System: Varati
Ship type: Flight operations
Dockable: Yes
Location: 822Ls from main star.
Distance from Sol: 213.21 ly

Survey Vessel Pandora

System: HIP 21478
Ship type: Unknown
Dockable: Unknown
Location: orbiting 1st planet
Distance from Sol: 289.44 ly

..

Survey Vessel Victoria's Song

System: HIP 17125
Ship type: Unknown
Dockable: Unknown
Location: orbiting 5th planet with purple rings
Distance from Sol: 354.94 ly

..

Overlook

System: HIP 22460
Ship type: Unknown
Dockable: Unknown
Location: [Permit locked system]
Distance from Sol: 362.01 ly

..

The Cete

System: Col 173 Sector LJ-F C12-0
Ship type: Unknown - Professor Melville's mega ship
Dockable: No
Location: find out when I get there...
Distance from Sol: 1,232.09 ly

..

Sagan Class Tourist Ship

System: IC 1805 Sector AV-O C6-6
Ship type: Passenger
Dockable: No
Location: find out when I get there...
Distance from Sol: 6,194.64 ly

..

Zurara

System: Syreadiae JX-F C0
Ship type: Cargo
Dockable: No
Location: find out when I get there...
Distance from Sol: 12,082.88 ly

..

Foster Terminal

System: Coeus
Ship type: Flight operations
Dockable: Yes
Location: find out when I get there...
Distance from Sol: 22,027.98 ly

..

This amazing new trailer for Elite shows off both the game (post 2.3) and the amazing new camera.

The trailer was created by the (clearly talented) CMDR Siledas using entirely in-game footage from his own game.

Hats off to you commander! Job well done.

UPDATED 11:36am

There is another BETA related controversy brewing. In the March 21st LiveStream, Frontier mentioned that the nameplates for ship hulls would be a purchased item.

What’s it all about?

In the next major release of Elite: Dangerous, a new feature will be ship naming. You will be able (in station outfitting) be able to set a name for each of your ships, which will appear on your HUD. You can also set a ship registry ID, which is your station traffic control call-sign. This name will also appear on other CMDRs HUDs when they scan your ship. This name will only appear on other players HUDs if you pay for a nameplate! The controversy is that most players assumed (right or wrong) that the ship name would appear on the outer hull of the ship by default, at no charge.

On yesterday’s LiveStream, Frontier instead said that the exterior nameplate would cost extra!

Now does that mean space credits or real-world wonga? It would appear to be the latter and that has got more than a few commanders hot under the visor!

CMDR Zeeman: I'm normally happy to support the FD store, but I'll be boycotting this, sadly.

CMDR BongoBaggins: Other CMDRs cannot see the name of your ship on their scanner unless you've bought a nameplate. That's not cosmetic DLC, its locking game features behind a paywall. It's opportunistic, mean-spirited and churlish, and I won't be naming my ships.

Back in the Design Discussion Forum (where ideas were spit-balled during the design phase of Elite) the agreed details on ship names were:

Ship Naming

• A ship can be given a name by a commander
• A ship name can only be registered at a reputable space dock
• There is a fee to register the name
• Names are not unique
• Although ships have unique registration numbers that can be shown
• Ship names can be changed using the same procedure
• By default a profanity filter is applied to all ship names (separate from chat filters) “starring” swear words out

The impression at that time was that the naming would cost credits in-game, but now Frontier have said it will be a cosmetic DLC purchase from the Frontier Store.

The most common reaction is disbelief:

CMDR Oryana: I wouldn't mind just a free basic name plate with generic font and no bells and whistles. I'd then probably pay for cooler fonts, or other colors or symbols next to it. The fact that I have to pay to essentially stencil on some letters on my ship is a joke.

Well respected streamer and member of the Elite community Obsidian Ant had this question:

If I buy a paint job for my Asp, I can use it on all my Asps. If I buy a name plate for my Asp, can I use it on all my Asp's? And if not, what happens to the nameplate when I sell that specific Asp?

Personally, I feel that a basic nameplate should be free and that more elaborate stencils should come with a charge, much as each ship has a free basic paint-job and further cosmetic customisation is paid DLC. As for not showing your ship name on other players HUDs unless you've bought a name-plate, well if that is correct, then it's an exceedingly poor and short-sighted decision.

Frontier have not responded on the thread. Frontier responded today at 11:03 (around an hour after I published this article!)

Edward Lewis posted this statement
Hi everyone,

There’s been a number of questions from Commanders regarding ship naming and how ship name plates will work so we wanted to give you a little more information about how these features will work when they’re released.

In-game ship naming

When you have named your ship in-game, your ship name will appear in multicrew grouping and in your HUD. In addition to this, in beta 5, when other people scan you, or target you in space they will be able to see your ship name in their UI. This feature will be available for all players of Elite Dangerous (both base game and Horizons players) including Xbox One, upcoming PS4 release and PC Commanders.

Cosmetic Ship Name Plates

The ship name plates will offer an added layer of cosmetic personalisation for Commanders wanting to wear their name with pride, much like paint jobs and other cosmetics currently available in the store.

Name plates will be made available in themed packs. These packs will contain three designs, each of which will be available in three colours: black, white, and grey. This makes a total of 9 nameplates per pack. After purchase, each pack will be available for use across all of your ships (Ship launched fighters and SRVs don’t have name plates) and each pack of 9 variant plates will be coming into store at just £2/€2.5/$3. This means that purchasing one pack of name plates will allow you to use that style across all of your current and future ships, at the same time and rename each individual ship as many times as you like. We believe this flexibility offers Commanders great value and is a great way to help support the continued development of Elite Dangerous.

Thanks!

So what do you think? Is this a micro-transaction too far? Or have Frontier made the right call?

EDIT: In light of the updated information provided by Ed, I would say that while the lack of a free basic name-plate is a shame, the low cost point for having name-plates across all ships answers most of the complaints. That and the clarification that the ships names WILL be visible to other players on their HUDs.

The third and fourth quarter of the year are set to bring us the most anticipated features of Horizons and some mystery as well.

2.3 – The Commanders - Coming Fall 2016

“Team up and stand together. Forge your own identity with the new Commander Creator, then share your bridge with Multi-Crew and fly with friends.”

We’ll be able to fly with up to three other human commanders aboard our ship, operating different stations – weapons, navigation, the pilot’s controls and ... what else? It has been said that a single ship with multiple crew-members would be “as formidable” as the same number of ships in a wing. How that could manifest will be interesting to see.
This update will bring us the commander editor, allowing us to make our own avatars with beards and big noses and with multi-crew, we’ll be able to show them off to our wing-mates.

I pause to wonder if features are gender locked; could I have a bearded lady avatar? Give me something to “hang on to” as Lord Flashheart would say. Lipstick and eyeshadow for the gents? Oh, eighties glam in the 34^th century!

At this point we cannot even guess how things like ship rebuy, or trade profits are handled when playing with multiple commanders on a single ship. How will the “guest” commanders get on board? Will we see them dock and walk into the cockpit, or will they just “pop” into existence? What do they see when boarding?

2.4 – ????

“A secret to be revealed in Elite Dangerous: Horizons’ final expansion!”

So, no idea on what the end-of-year update will bring. Sandro shirts for your Avatars? A bobble-head of your own ship? Tractor beams? Weather on planets? A ships cat? Zero-G cat litter. Maybe not.

What would I like to see? Ship-to-ship docking; not boarding at this point, just docking. Why? Mega-ships, too large for stations could be docked with, to exchange cargo/passengers. This would make the “seeking goods” ships more hands on. We could take guests to that wedding we keep hearing about. Explorers could dock with mega ships that are “mobile outposts”.

I guess we'll have to wait until November to find out!