WiFi Radar is a nifty little GUI program that lets you switch wireless networks with ease.
The project's documention gives a good overview for the user interface.
wifi-radar needs to be run with administrative privileges. Edit
/etc/sudoers using the visudo command and add:
yourusername ALL=(ALL) NOPASSWD: /usr/sbin/wifi-radar
Then, run wifi-radar from your application menu to view the available networks or to configure your setup.
For configuration file options, see the project's manual.