I use a DENEB USB card and a NetGear 10/100 usb dongle with mine. It's an older model before they shrunk down to the size of a USB stick, but I believe there are a few others that will work also.
I'd really like to find a wireless USB stick that will work with the USB stack but from what I have heard thus far, the newer chips they use are not supported... plus I suppose we'd need a WiFi prefs tool as well so I guess it makes sense.