Yesterday's release of arouse a long discussion among some users. Today we're posting [url=http://www.gog.com/en/editorial/editorial_smoke_mirrors_and_the_phantasmagoria/]an article by David Craddock which shows the history of the game and we hope will clarify some doubts.
In the early 1990s, famed Sierra On-Line co-founder and game designer extraordinaire Roberta Williams, who had conceptualized and designed many of Sierra's biggest hits including the critically and commercially successful King's Quest series, was familiar with the phantasmagoria shows of yore. Delighted with their dark tone and eager to delve into the realm of terror, Williams began plotting a new adventure game with a horror theme. The name of the title would be Phantasmagoria, paying homage to the eponymous theater productions.

Eidos: (or at least I think they were from Eidos)
Thief The Dark Project (or Thief Gold)
Thief 2: The Metal Age
System Shock
System Shock 2

MobyGames is a resource for looking up the publisher details.

*nod*
Also, Tomb Raider series (first five or six games), Micro Machines series (first three games), Commander Keen series (including episode six, if possible), Rollcage series, KKND series, Urban Assault, Galapagos, Gorky 17, Flashback and Jagged Alliance 2 seem reasonable. And I'd love to see some arcade and console ports (Metal Gear Solid, Resident Evil and Final Fantasy kind or some more bizzarre ones) in here. I'll try to think of some more.
And by the way, there is another topic dealing with exactly the same thing. It has some good ideas, too, such as Little Big Adventure (a.k.a. Relentless: Twinsen's Adventure) and its sequel. Maybe all these lists should be united in a regularly updated post?

MicroProse Software, Inc.
Worms Armageddon
Titus France SA
Worms World Party

Published by Strategic Simulations, Inc and developed by Westwood Studios
Eye of the Beholder series
Published by Psygnosis Limited and developed by FTL Games
Dungeon Master
Pleeeeaaaaaaaase! :p

Sierra:
Arcanum!

Midway Games / Acclaim
Mortal Kombat series
LucasArts
Monkey Island series
Sierra On-Line
Leisure Suit Larry series
ID Software
Doom, Quake series
Team17
Bodyblows series
Capcom
Street fighter series

Eidos:
Deus Ex!

I agree with all the suggestions so far. Here are some others that haven't been suggested yet.
Toys for Bob / Accolade
Star Control
Star Control II
3D Realms
Duke Nukem 3D
Westwood Studios
Blade Runner
Cryo / Virgin Entertainment
Dune
Interplay
Star Trek 25th Anniversary
Spectrum Holobyte / MicroProse
Star Treck the Next Generation: A Final Unity
LucasArts
Tie Fighter
X-Wing
X-Wing Alliance
Electronic Arts, Inc., ORIGIN Systems, Inc.
Wing Commander
Wing Commander II
Wing Commander: Privateer
Activision
MechWarrior
MechWarrior 2
MechWarrior 2: Mercenaries
MechWarrior 3
MechWarrior 4
NovaLogic, Inc.
Tachyon: The Fringe

Virgin Interactive
Ignition
Activision
Tony Hawk's Pro Skater 2
GT Interactive
Driver

(I am supposing that this would be for any publisher - Not just ones currently within GOG)
Bethesda Softworks/Zenimax Media
The Elder Scrolls II: Daggerfall
The Elder Scrolls: Legends: Battlespire
The Elder SCrolls: Adventures: Redguard
Electronic Arts
The Ultima Series.
Lucas Arts
Jedi Knight Series (Mainly the Dark Forces 2 expansion - Mysteries of the Sith)
And many, many more that I can't think of at the moment.

Just as Kunikos suggested I would also looove to play these gems again:
Crusader: No Remorse
Crusader: No Regret
Another game I really miss from the good ole days is Hardwar

Pretty much everything that was already mentioned, plus:
Sierra
King's Quest series.
Also, old side scrollers, like Flashback, Another World, old Prince of Persia series, etc.