Etymotic ER-4S rules for playing any Half-Life game, especially Counterstrike, since you can very, very precisely place people by their footsteps even if they're behind walls. Their $250 price tag (from ToddTheVinylJunkie.com ) may be a bit high for you though. However, I don't think there's a better CS headphone out there, period. Not only do they have incredibly precise imaging but you'll be able to hear every nuance of someone inserting their clip into their gun, much less tell when they're reloading.
Oh, and they sound damn good too. To be honest, I'd sell my $7500 (retail) Sennheiser HE90s before I sold my Etys. (to be fair, the Etys are a lot more practical in a general-purpose headphone kind of way; they don't need a $1000 electrostatic headphone amplifier. You will want to pick up a decent amplifier from Todd or JMTAudio.com though.)