Aha, fortunately the latest Linux Magazine in England has just had a feature on this. Apparently one of the best supported is the Lancom cards (both PCI and PCMCIA).
They say the AirLancer MC-11 is a good PCMCIA card or the intel PRO/Wireless 2011b LAN PC card. They both use the Prism 2 chipset and the hermes orinoco and orinoco_cs modules get loaded automagically (I've never set one of these up before so have no idea what this means. Try a google search or something like that).
For the intel card you need a firmware update from www.red-bean.com/~proski/symbol