USB 1.1 or USB 2.0 ?
2, 3, or 4 ports ? (some have extenstions for more)
Included Firewire ?
Which brand name ? (or which is cheapest?)
Pricewatch can help with the price as you start to answer the other questions.
If you want to buy online use Reseller Ratings to check out the companies reputation. Otherwise 9 out of 10 of the USB PCI card products listed on Pricewatch can be found in your local Compusa, Fry's, or BestBuy... not to mention your local mom'n'pops (these will likely be non-branded equivalents)
not trying to ask a dumb question, but does your mobo have usb expansion on it? Cause then you wouldnt need a pci usb card. and you could mod the case and run the usb to the front or side.