MacStumbler 0.7
If you want to check out what wireless signals abound as you travel around, MacStumbler 0.7 is the ticket. The latest version adds GPS (Global Positioning Satellite) support so that as it finds and logs access point (base station) details, it can put a virtual pin at a point.
Network administrators have long found the 'stumbling programs useful, as they help plan service areas, chart obstacles to signal strength, and find rogue wireless base stations. Those of us with no system admin duties like to see how many people are using Wi-Fi -- and whether we can hop on for a few minutes of email. Not that I advocate that.