Thumbs up for the M-Audio Delta and Audiophile cards.
Another card worth looking at is the Emu 0404.
http://www.dv247.com/invt/22115/
A brief word of caution: Like some other musician/audio production oriented cards it does lack full support for some older games if you play them. You can overcome this by keeping your existing card enabled and manually switching between the two as your default playback device for compatibility's sake.