I believe NetStumbler can also auto-configure your system based on the networks it sniffs. I haven't used it but I've used the PDA version (MiniStumbler) which had this ability.)
You can also buy a stand-alone Wi-Fi detector. The best one IMHO is the ZyXEL AG-225H. Locates wireless networks, shows you the signal strength & level/type of encryption, recharges from the USB port, acts as a USB wifi adapter and will even serve as a mobile wifi access point. Its the wifi Swiss army knife!