The real gems that I was not able to find.
Imperialism 1 & 2
http://en.wikipedia.org/wiki/Imperialism_%28video_game%29
Especially the first is a true sim game gem that runs at least under XP right out of the box.
http://www.youtube.com/watch?v=o2MH4mwRpp8
Fugger 2
http://de.wikipedia.org/wiki/Die_Fugger_II
I do not know if an English version exists. It's the predecessor of http://en.wikipedia.org/wiki/Europa_1400 IMHO it is still the best game of the whole serie. Unfortunately it is a dos game.
Other games that would be nice:
SimCity serie
Trade Empires
http://en.wikipedia.org/wiki/Trade_Empires
Merchant prince series
http://en.wikipedia.org/wiki/Merchant_Prince_%28series%29
Anno serie
Railroad Tycoon
Age of Empire 1

I would love to see the Blood Omen: Legacy of Kain games and the Soul Reaver ones as well.

id Software's games need to be on here. They are the kings of classic FPS.
- Commander Keen 1-6
- Wolfenstein 3D, Spear of Destiny, The FormGen Mission packs, Return to Castle Wolfenstein.
- The Ultimate DOOM, DOOM II, Final DOOM, Master Levels for DOOM II, maybe even DOOM 3 w/ Expansion?
- Quake w/ both mission packs, Quake II with both mission packs, Quake III + Expansion.
I bought the Quake games on Steam, and to my disappointment, they are missing the music. That's a crime.
Raven Software has titles that belong on here too. Heretic: Shadow of the Serpent Riders, HeXen + It's expansion, Soldier of Fortune 1 + 2, etc.

Chicago 1930
GOG, pleazzzzzzzzzzzeeeeeeeeee!!!

Here is a list of some classics that would definitely fit here :
. Blade Runner
. Deus Ex
. Legacy Of Kain games (espcially the first Blood Omen and the first Soul Reaver)
. Little Big Adventure 1 & 2
. Max Payne 1 & 2
. Tomb Raider 2
. Flashback : The Quest For Identity
. Omikron : The Nomad Soul
. Resident Evil 1, 2 & 3
. Classic Star Wars games like : Dark Forces, Jedi Knight : Dark Forces 2, Jedi Knight : Mysteries Of The Sith, Rogue Squadron 3D, Shadows Of The Empire, X-Wing Alliance, etc...
Now, a few words about some less popular ones, but great nonetheless :
. G-Police : futuristic helicopter simulation in a Blade Runner-like universe with great atmosphere, storyline and cutscenes.
. Overboard ! : first 3D game I've ever played ! Sail a pirate ship and fight your way through colourful levels (there's also a fun multiplayer mode).
. O.D.T. : Escape Or Die Trying : a interesting mix of action, adventure, shooter, puzzle-solving and RPG set in a steampunk world with a gloomy atmosphere.
. Comix Zone : classic "street fighting game" set in a comic book... It's short (6 levels) but the game is quite hard and offers an interesting challenge.
. Dino Crisis : it might be a "Resident Evil with dinosaurs", but it is a good one. Do not compare it to Dino Crisis 3, which is awful and almost unrelated.
. Dark Reign : I'm really not into RTS games, but this one left a good impression on me, even though I've never been able to get past the fifth or sixth mission (I suck at RTS games)
. Rayman 2 : The Great Escape : I was a bit surprised to see that the Rayman games had very little votes. I think they were made by Michel Ancel, who created Beyond Good & Evil.
Now, those I never played :
. Shadow Man
. Rayman
. Bioforge
. System Shock 2
. Crusader : No Remorse & Crusader : No Regret
I was wondering... Do votes have any influence of some sort ? How do the GOG team choose their games ?

The Last Express!

Now that would be instabuy to end all instabuys.

Hell feckin yeah!

Ecstatica 1 and 2.

I'd like to second Z and Steel Soldiers too (although I never got to play SS).
I'd also like to second Blood Omen: Legacy of Kain
I've read Blade Runner from a couple people. It would probably make a nice addition though my desire to play it again isn't that great for some reason.
Here's a few more I'd like to see:
Silver
Revenant
Myth
Quarantine (Took me forever to remember its name! I loved this back in the day. If you don't know this game, look it up!)
Alien vs. Predator

Well, since the Total Annihilation request went down so well, let me also request the Bard's Tale Series. You've probably heard of an old series of roguelike games by that name, but I'm particularly interested in the 2004 game based on the older trilogy.
Also, I'm still wishing for Crusader: No Remorse and Crusader: No Regret.

Dungeon Keeper 2. Please.
Syndicate Wars. Please oh please.
Only one mention of Startopia so far, so here I am begging. Startopia, please please please. I think it is one of the old games that really fit in GoG: good gameplay and unique design which was not really appreciated at its time, and much more. In the game we manage this torus-shaped space station, we build on each floor and each section and make it so interesting that aliens will visit and start living in there. From the love salon to biosphere, we cater to all the alien needs, be ready for solar flares and catch its energy to power many functions of the space station, and also frequent visit from Arona and his (or her?) cliche but fun jokes. I imagine this is one place that should be included in Douglas Adam's Hitchiker;s Guide to Galaxy, if Mr. Adams happen to play a computer game. So many good memories!
And also Little Big Adventure Series 1& 2

Would not mind seeing Cossacks on GOG.
I second Imperalism.....the First one in particular.
I would love to see Dungeon Keeper also, but EA owns the rights to Dungeon Keeper which means we will see it on GOG about the same time we can play a game of Ice Hockey in Hell.

The two series I see missing (although maybe the entire publisher isn't available):

The Legend of Kyrandia 1-3
Lands of Lore 1-3

Is Westwood just not an option? So sad if true...

Oh, and Quest for Glory? King's Quest and Space Quest, but no Quest for Glory? I has a sad. :(

I'd love to see both of the System Shock games on here. I'd snap 'em up, day one.

Kyrandia for the win! I totally want to play those games again.