I think as a general rule of thumb a PCI card would be best.
I can definately recommend the Netgear WG311T, I'm using one which has an Atheros chipset.
Have a good search to see if you can find recommended one's. The thing is that sometimes the manufacturer changes chipset and makes a new revision, so a version 2 card might be Atheros based, but a version 4 might be something else.
Either way, failing native support, Ndiswrapper is quite good..