Any card that uses the Prism-2 chipset (most cheaper ones) will work with the mimimum of hastle using the Linux-wlan drivers.
Look at D-Link's and Linksys as these are all Prism-2 AFAIK
However I've only tried on laptops so you may want to verify that the PCI-PCMCIA adapters often supplied with PCI versions also work (I think they are pretty much a "straight through" device so should be no problem).
Wayne