Well, I'm not at it at the moment, but off the top of my head (ignore the lack of alphabetical order)...
Alien Swarm
Alien vs Predator Gold Edition (which won't work)
Alien vs Predator 2
Counter Strike
CS: Source
Half Life (+ Blue Shift & Opposing Force)
Half Life 2
That Half Life 2 bloom demo
Portal
The Path
The Dig
Loom
Indiana Jones & the Fate of Atlantis
Indiana Jones & the Last Crusade: The Adventure Game
Day of Defeat
Call of Cthulhu
Knights of the Old Republic 2
Deus Ex
Deux Ex: Invisible War
Sid Meier's Pirates!
ArmA
Robinson's Requiem
Deus
Gothic
The Guild
Lure of the Temptress
Beneath a Steel Sky
Jagged Alliance
Jagged Alliance 2
Realms of Arkania: Blade of Destiny (but I can't get past the first damn dungeon!)
Realms of Arkania: Star Trail
Uplink
UFO: Enemy Unknown
XCOM: Terror from the Deep
XCOM: Apocalypse
Warhammer 40K: Dawn of War (+ the first two expansions I can't remember)
Fallout
Fallout 2
Fallout Tactics
Fallout 3
Vampire the Masquerade: Bloodlines
System Shock 2
Hitman: Blood Money
S.T.A.L.K.E.R.
Neotokyo
Garry's Mod
Diablo II (+ Lord of Destruction expansion)
Minecraft
Team Fortress II
Cave Story
Supreme Commander
The 7th Guest
The 11th Hour
The Feeble Files
Battlefield 1942
Battlefield 2
The Sims 2
The Sims 3
SWAT 3
Theme Hospital
Dungeon Keeper II
StarTopia
Silent Hunter III
Blood Bowl
Chaos League
The Elder Scrolls I: Arena
The Elder Scrolls II: Daggerfall
The Elder Scrolls III: Morrowind
The Elder Scrolls IV: Oblivion
Bunny Must Die
And this doesn't include the Commodore 64, Amiga and DOS games I emulate.
*EDIT* 70 games, probably with many more I've forgotten...something tells me I have too many games.