I'm setting up Raspberry Pi's using the Edimax EW-7811Us wifi module available on Amazon for a mere $11.
Following the Debian WiFi wiki page initially didn't work.
The EW-7811Us uses an RTL8188CUS chipset which requires the rtl8192 kernel
driver. There's no
firmware-realtek package on Raspbian, and the best
answer I found was to download some dude's hacked kernel module. No thanks.
Instead, install the
rpi-update package then run
rpi-update. The firmware
will be updated in a way officially supported by raspbian (if there is such
a thing). Then reboot.