Edimax USB Wi-Fi Adapter $18
Currently one of the smallest USB wi-fi adapters, this little networking dongle plugs into the USB port of your Raspberry Pi and connects you to your wireless network at home, school, work, or your local hackerspace. Unlike a many other larger USB wi-fi adapters, this one is ready to roll with the drivers already packaged with most major Raspi Linux distributions. It’s also very, very cheap at under $10 from many retailers, making it a perfect stocking stuffer.