I just purchased a D-Link DWL-122 USB adapter for $44 shipped and
there's a $10 MIR, so it'll come to about $34 when I get my $10 back. I
just plugged it in and fired up KisMAC and it's scanning! Cool! Now I
don't have to worry about the driver messing up my Airport card and
having to reboot to get back onto a network.
It also includes a driver for OSX to use it as a network adapter. The driver is a little goofy, it has its own control panel in System Preferences. The control panel is also a bit too large. Once you use their driver and hit Connect, you have to go to the Network control panel and it will detect the new ethernet adapter and you can set it up. Or at least that's what I did.
If you try to scan in KisMAC after you have set up the USB device as an active network adapter, KisMAC will shut down the D-Link driver, but it won't be able to launch its own. All I had to do to fix that was to unplug USB device and plug it back in while leaving KisMAC running, then click the Scan button again and KisMAC was able to start scanning. After KisMAC quits you have to unplug/replug to get the D-Link driver to restart.
My plan is to rip it apart and attach a cantenna to give to my girlfriend. I haven't yet figured out if I'm going to be able to remove the plastic case without damaging it. It's a keychain fob sized unit, and I can't find any screws holding it together. It might be glued.