Miniature WiFi Module for Raspberry Pi
Description: Make your Internet of Things device cable-free by adding WiFi. Take advantage of the Raspberry Pi and Beagle Bone's USB port to add a low cost, but high-reliability wireless link. We tried half a dozen modules to find one that works well with the Pi and Bone without the need of recompiling any kernels. You'll have wireless Internet in no time at all! Works great with 802.11b/g/n networks.
Please note: The WiFi module may look slightly different than above, but all modules shipped are Pi-tested and contain the same chipset and have equivalent performance, the only difference is the plastic shell.
A useful blog on getting it set up