When you get into nice cards, they automatically come with 5.1 or 7.1 capability. I would recommend a Creative Audigy2 ZS. That's what I use and its amazing. Its 24-bit 192kHz with a 108 S/N ratio. Talk about clean, this card is pure heaven. It has a lot more features then you'll need, but you might find yourself using more than you think after you start playing with it. It also supports DVD-Audio, which is awesome.
You can find the Creative Sound Blaster Audigy2 ZS for about $75 from newegg.com and other online retailers.
Here's a link to Creative's website.
http://www.creative.com/products/pro...5&product=4915