Arguably, some of the worlds finest up-and-coming-composers have cut their teeth on video games, Steve Jablonsky comes to mind, responsible for the first three Gears of War games and all three Transformers movies among others.
Left 4 Dead was a pretty decent game, setting aside the creeping horror for pure unadulterated action and whilst it missed the mark for many purists, it's a popular franchise for good reason, you get to shoot lots and lots of zombies... make that gazillions of zombies!
Mike Morasky's themes are dark, sinister and there's some wonderful use of piano and bluegrass guitar that gives it a small-town American feel form time to time. Pretty much all of the tunes are worth adding. I even like in game recordings from Left4Dead 2 from the Midnight Riders. Last seen somewhere near the whispering oaks fairground. Check out their website for more info.
To finish off, here's another track from me back in 97. Entropy - Machine.