I stopped by Office Depot today to buy a wireless usb card. I wound up getting the rather generic sounding Ativa Wireless G USB network card. This turns out to be a rebadged Belkin F5D7050 v4000 wireless card. This has the ZyDas ZD1211 chipset in it. This is a fairly popular chipset to judge by ebay (where it is just about the only chipset advertised).
There's a Linux driver. Well, there are two. One that was basically binary only that was written by ZyDas, and another that was a rewrite by the community. I'll have to see if there's one for FreeBSD :-)