The RT2400 and RT2500 chipsets are possibly the only WirelessChipsets with a GPL driver
"Ralink worked with Mark Wallis, Ivo van Doorn, Luis Correia, Robin Cornelius and others to get a supported driver out there under the GPL". "Special thanks to Minitar, the network gear vendor with the foresight to ask Ralink to make the driver GPL".
4 pages link to RT2x00WirelessChipset: