Combination WiFi + Bluetooth 4.0 USB Adapter : ID 4827 : $14.95 : Adafruit Industries, Unique & fun DIY electronics and kits
Mini USB WiFi Module - RTL8188eu - 802.11b/g/n : ID 2810 : $11.95 : Adafruit Industries, Unique & fun DIY electronics and kits
TiVo WiFi 5 USB Adapter
Pololu - Wixel Programmable USB Wireless Module
EEEkit 5.8G 433Mbps/2.4G 150Mbps Mini Wireless Dual Band WIFI USB Adapter with Antenna Network Dongle for PC Laptop - Walmart.com
Amazon.com: NETGEAR WG111US Wireless G USB Adapter : Electronics
USB WiFi (802.11b/g/n) Module: For Raspberry Pi and more : ID 1012 : $13.95 : Adafruit Industries, Unique & fun DIY electronics and kits
Cables Unlimited Wireless USB Adapter Kit Review
Internal USB B/G Band WiFi Module with IPEX antenna connector
Amazon.com: USB WiFi Adapter for PC, 1200Mbps USB 3.0 Dual Band 2.4Ghz/5Ghz WiFi Dongle with Dual High Gain 5dBi Antenna and USB3.0 Dock Wireless Network Adapter for Desktop/Laptop Supports Windows/Mac OS/Ubuntu :
Linksys WUSB6400M USB Wi-Fi Adapter
Pololu - Wixel Programmable USB Wireless Module (Fully Assembled)