If you are looking for a Display card to go with the system then I recommend the Matrox cards, G450 or G550.
I had bad experiance with the rest, except the G-Force 4 that I fully intend to try soon.
If you are looking for a Capture/Edit card you will have to give little more info -
Do you need Analog in as well as the DV/Fire wire you allready have ? How mush real time are you looking for ? Are you looking for a card that can excelerate Mpg2 exports for DVD ? Price range and such...
I have a review of the Pinnacle Pro-One Vs. Canopus DV Storm at my site. You might want to take a look at it.
Intel / AMD - <A HREF="http://www.llnl.gov/asci/news/white_news.html" target="_new">IBM are still the best</A>