I recently acquired a Raspberry Pi, and have installed Debian Squeeze on it, and after doing a small bit of research (I'm not too proficient with Linux) I found and ordered a USB wireless dongle ("LevelOne WUA-0605 N_Max Wireless USB Adapter") that appears to have support for Linux.
This is the page I found that looks like it says the dongle has a Linux driver. I installed (what I think) was the driver package,
firmware-ralink. Now I'm not sure what i need to do to make it work.
lsusb lists the device as
Bus 001 Device 008: ID 0bda:8172 Realtek Semiconductor Corp. RTL8191SU 802.11n wLAN Adapter