Vistumber v8.1 is an excellent, free tool for finding nearby wireless access points, and giving you a great deal of information about each. It's much like the popular NetStumbler program, except appears to work with a wider variety of hardware.
Tell the program to scan for nearby wireless networks, and it gives you a comprehensive report, including the name, signal strength, kind of encryption, Mac Address, channel the network is using, manufacturer, and more. It will also graph the traffic for each network as well.
If you want to use the most sophisticated features of the program, you'll need a GPS attachment for your laptop, and you'll need to download extra software. If you do, claims the author, you'll be able to map the nearby wireless networks it finds onto a map of Google Earth.