WiFi Radar is a free easy to use tool that allows Ubuntu users to scan for available wireless networks via a GUI. It also allows to connect and reconnect rapidly to any network of your choice.
The user interface for WiFi Radar comprises a lot of options such as configuring the network name, network address, WiFi security (WPA/WEP), selecting channel, key, DHCP or fixed IP, etc.
WiFi Radar is available in the Ubuntu official repository, you can simply install it on Ubuntu 11.04/10.10/10.04 with this command via the Terminal:
sudo apt-get install wifi-radar
To start it on Ubuntu 10.04/10.10, open Applications > Internet > WiFi Radar, and on Ubuntu 11.04, search for it using the dash. Or simply start it via the Terminal with this command:
WiFi Radar's screenshots: