iStumbler is a powerful free tool for finding and troubleshooting wireless networks. It will display all the wireless hotspots within range of your Mac. You can quickly determine whether they’re open or secure, their SSIDs, signal strength, the wireless channel used, and more:

iStumbler Website

This type of information is becoming increasingly important in some Seattle buildings were dozens of wireless networks compete for bandwidth. It’s also a handy tool if you find yourself away from the office and hunting for a free hotspot to check email.

Source: This tip inspired by an increasing number of challenges establishing stable wireless networks in active areas of the city. Recently one client found himself in a highrise with over 22 other wireless networks.