I would love to see Ripley's Believe It or Not!: The Riddle of Master Lu. It was a great adventure game. :D

I want Metal Fatigue dammit!

command and conquer gold for win95 was released for free.

and tiberian sun as well.

System Shock 1 & 2

The Neverhood

Warhammer 40k: Chaos Gate, Final Liberation, and Rites of War

Mechwarrior 2 & 3

Outlaws

Still.. All Discworlds.

I have looked for these 2 games for years. It would kick butt too play them again!!

Privateer 2 for sure!!!!

Full Throttle!!!!

Aliens vs Predator 1 and 2

Theme Hospital

Doom I & II (Doom II is already abandonware)

Legacy of Kain: Blood Omen

Lucasarts adventure games(hardly possible, but would love to play Curse of Monkey Island and Loom sometime)

Age of Empires (Not really feasable as it is owned by Microsoft game Studios)

Rise of Nations Finally one that I would definitely pay for is Rise of Nations!!!!!!! This game is LITERALLY NOWHERE to be found nowadays.

Worms!!!!! (also Liero would be a good choice for 5,99)

Penumbra ( not that old... but it is definitely a GOOD GAME, besides, I'm pretty sure the GOG userbase would like this game)

Red Faction (ph yes...come on)

The Neverhood I know some people remember skullmonkeys, so why not?

GUBBLE: Finally... I would actually pay to play GUBBLE again...(yeah, I'm pretty sure I've made some fo you google that, but trust me, nostalgia overload will be worth it)

I'm not mentioning the games everybody has always mentioned (I'm looking at you System Shock), and I would love if some people agree with my choices.

Battlezone (1998). Fun hybrid of a tank simulation game, a first-person shooter and a real-time strategy game. The best part was how it all worked together quite well.

Warhammer 40k: Chaos Gate. A very good tactical squad game using the always fun Warhammer 40,000 IP.

I would LOVE to see Syndicate Wars on here (and also Syndicate). I bought Syndicate Wars years ago and never got around to completing it, but I think it was a fantastic game.

Also Theme Hospital.

Please! :D

Theme Hospital...that is pretty much the 'big' one I have wanted since I have been on the site (3 years and waiting) :P

Activision Battlezone I&II (Oh, please)

Syndicate

MechWarrior 2 & 3

MechCommander

I would love to see MechCommander 1&2 on gog.

Personally, I would love it if GOG struck up a deal with Falcom to release localized versions of the Ys series. There is about 7 or 8 different PC games from that series, and it shouldn't be hard to arrange for localization if GOG can permission from unofficial translators to use their work. It would also be nifty if Capcom could release their Phoenix Wright games via GOG, too.

EDIT: Oh, and to release versions of Snatcher and Policenauts. Both of these games were made by Hideo Kojima, the guy who made the MGS series. I would argue that these are actually superior to his MGS work, largely because they are self-contained stories.

I'M BAAAACK!

Some more I was thinking about that I totally neglected to mention:

Sid Meier's Colonization
Man, I played this game solidly for a couple years straight and would come back to it constantly until it no longer ran on my newer systems. Now, that being said, there IS a version out fanmade, I believe but it's pretty buggy. Getting the classic version with the GoG treatment would be freaking awesome and an instant buy for me.

Sid Meier's Civ 1 and 2 with Civnet ofc. :D
Do I really even need to add a reason why? ;)

I Have No Mouth and I Must Scream
One of the most disturbing games I think I've ever played and a must have for any adventure gamer out there. (As long as you're not squeamish.)

Starz
If you're not into ultra deep 4x strategy TBS games, then this probably isn't for you, as it's not very graphically pleasing. Yet somehow, even as dry as the presentation was, it had that "just one more turn" factor that kept me clicking long into some late nights.

Avalon Hill's Advanced Civilization
If you're not into the type of games that AH's foray into computer gaming offers, then this MAY NOT be for you, but I enjoyed it immensely, even if it did feel a little like a straight board game port. (Hey, it worked for Risk.)

Inca 1 + 2
Was a pretty under rated adventure from an era when Sierra pretty much owned the genre.

Warhammer Shadow of the Horned Rat and Dark Omen
Both excellent fantasy strategy games. Build your armies up, earn money from winning battles while taking the least amount of casualties possible, use battle magic to increase your odds of winning. Setup spear pickets for your ranged units and send cavalry into the enemies' flanks!

I'm sure I'll be back again when I think of a few more. :D