I myself asked the same question over on etree a few months ago. I ended up with an m-Audio DiO2496. It works great, easy to install. Can use the internal clock or the incoming S/PDIF signal.
Got mine on ebay for $140. You can get them new from Guitar Center for about that same price, supposedly.
There is only one drawback. There are no analog input. Read again. No analog input. Now I am in the hunt for another solution to that, and it is not that easy.
Good luck,
make sure you get what you need.
UJ