Level One USB Wireless
The specs on this are actually really good. It has a ZaDAS chipset which is fairly compatible and has drivers for more OS's than Level One indicates. Whether or not they work is another story!!! See ZyDAS chipsets based wireless 802.11a/b/g devices.
A Google Adwords link on that page caught my eye and found this really cool page on
MiniPCI chipsets. Not entirely sure about what they do, but they seem to have extensive drivers for minipci wireless chipsets, which is cool.
I also found another webpage purporting to have OS X (10.4+) drivers for this USB WLAN adapter:
OS X 86 Project Page about Drivers
They point to:
Link to Disk Image of drivers.
Also found these helpful pages:
Ralink Drivers
Zyxel Drivers
Airport Blog
I was able to install some drivers for Mac OS X 10.3, but they don't work very well. Lot's of errors, and unstable behavior.