Anarchemitis said:
Half-Life 2's 'Requiem for Ravenholm' stung me well, but I'd also go with 'Sector Sweep' from Episode 2.
Is Sector Sweep the one they used in the Ep2 Trailer? Cause that song is awesome. Alot of the Half life 2 music is great. My fav is VLVX_song_23, though (sorry only know them by their file names).
Braid has some really nice music, mainly the menu theme, and the theme for world one, those are both pretty tight. "4000 Degrees Kelvin" as well as "Still Alive" (both from portal) are very very awesome. Unreal Tournament's Hyper Blast Redux is also great.
But the very best music in a game is the Bejeweled 2 soundtrack. That, is what God sounds like, were he/she/it a song.