M-Audio products are recently Vista compatible. They tend to have very good sound quality and stable drivers. A very common soundcard solution is the Audiophile 2496 (from the Delta family of soundcards). 64 bit drivers are on the way if they aren't already here.
You make an excellent point for not buying M-Audio products. Hold up before you get too irate!! I'll explain myself:
Vista has been out for over 1 year at this point. Yet there are still no drivers for x64. I wonder: How long did they take to roll out x86 drivers for Vista?
If you had a Creative Labs product, you would have had complete driver support before Vista reached RTM.
I'm not saying that your audio card isn't super-high-quality. But unless you're an audiophile or audio-professional... the extra quality/power is neither noticable or needed. On the other hand, a possibly over-priced lower-quality soundcard from a company like Creative Labs will ensure that your card will work with just about everything. They're just so ubiquitous with computer audio ... you know it will always be supported.
Just my $0.02. I'm not an audiophile or audio-professional, though.