Outside with your laptop and NEED to find the internet? If you're on a Mac, iStumbler can help you feed your internet addiction.
If you're inside and curious what networks reach your apartment, it is a great little tool. It reports which ones are open, and the strength of the signal. iStumbler works with bluetooth signal as well, so it may help diagnose how far you can work away from a device. Oh, and its free.
We're sure this is not the only program on the market that does this, let us know in the comments if you have a favorite Mac or PC program that helps you out in your quest for wifi.