Hi Steve,
There are many cards that have a digital out on them. The choice comes down to some other things.
1) Do you need an optical out or coax out?
2) Are you also going to be using your PC for gaming?
3) Budgetary constraints
There are some cards that have optical out, but the majority of cards that support digital out have coax.
If you're into gaming as well as Home Theater then the SB Audigy cards are quite good.
If you're more into pure Home Theater but still on a budget the M-Audio Revolution 7.1 is a good card.
And there are a thousand other options!
If you want to research it further, do a search over at AVSForum in the Home Theater Computers area. It's a veritable goldmine of information over there.
Here's the url...
http://www.avsforum.com/avs-vb/
Good luck!
Roscoe