The Old D&D Gold Box games by SSI Dragonlance and Dorgotten Realms game.

the quest for glory series

Mechwarrior 2 ( and/or Mech2: Mercenaries)
Would *love* to play this multiplayer again...

Broken Sword 1 & 2
Warcraft 1 & 2
Starcraft
Planescape Torment
System Shock games
Divine Divinity
Monkey Island games
Stronghold
And try to add Final Fantasy games, especially Final Fantasy VII! I've never played in compatible and unbugged version on PC! Get to work GOG. ;)

Personally, I'd love Pharaoh, Crimson Skies and the early Midtown Madness games. They're pearls.
Kotor, Planescape Torment, Outlaws, System Shock II, Dungeon Keeper 2, and last but not least; JAZZ JACKRABBIT 1&2. They are so much win that I'm willing to pay for them despite them being abandonware. wryyy

someone have already said Jazz jack Rabbit and Tenka ?

First off, it seems there's a desperate need to do this in a more organized way, preferably one that doesn't involve the CDProjekt guys scanning posts manually to generate statistics. A poll of some kind, perhaps?
So, on to the actual games:
- King of Dragon Pass: it's a unique game, and the only way you can buy it now is by bothering their customer support for a copy - not exactly ideal.
- Arcanum: self-explanatory, I believe. If it came with Drog's unofficial patch, even better. Maintaining compatibility with it would be necessary in either case, it really fixes lots of issues with the game.
- Outcast: a forgotten gem, a PC game that has not been surpassed in some ways even to this day. This is how an immersive, cinematic game should be done; not just focusing on graphics, but paying attention to NPC behaviour, lore, and minimalizing meta-game aspects.
- X-Com: Not sure whether it's even possible now that it's on Steam, but it would be a nice addition. I know I would pay that whole extra $1 to not have to deal with Steam's DRM, anyway.
- Dark Omen/Shadow of the Horned Rat: Almost forgot these. Great games, with painful compatibility issues.

I forgot a couple:
- SSI Goldbox games
- Wasteland

Baldur's Gate & Icewind Dale series + expansions
SystemShock series
Tex Murphy series: Mean Streets, Martian Memorandum, Under a Killing Moon, Pandora Directive, Overseer (big downloads)
Alone in the Dark series
Magic Carpet series
Little Big Adventure Series
Bad Mojo
I Have No Mouth, and I Must Scream
Jazz Jackrabbit
Dark Forces
Jedi Knight + expansion
Neverhood (I still have to CD haha!!!!)
Entire LucasArts adventure library (I own all these too hahahaha!!!!)

I would like to see Elite 2: Frontier and Elite 2: First Encounters.
Would be fun to see old Dune 2, or Dune 2000.
The old game "Z" and Little Big Planet.

Definitely Starcraft and Brood War.

yea it will be great too to bring the good oddworld

Warcraft 3
Warcraft 3: The Frozen Throne
Call of Duty 1-2
C&C: Red Alert 2
Monkey Island games
Dungeons and Dragons

Myth 1, 2, and 3
entire Legacy of Kain & Soul Reaver series
////
you can get these at BestBuy and Walmart

-Blood Omen
-Dark Earth
-Anachronox
-Gabriel knight
-Septerra Core
-Requiem: Avenging Angel
-Urban Chaos
-Tachyon
-Heavy Gear
-Alone in the dark