I hear good things about the Auzentech soundcards. I really can't see any way to justify $150+ for a sound card though. Especially now since digital output is so common fancy SNRs, frequency response, harmonic distortion and all of that jazz doesn't mean anything.
Basically, all that matters is how much it affects performance, whether it has the features that you want, and the implementation of EAX-style effects.
You'd be a lot better off spending the extra money on speakers.