The Mac airport utility will automatically detect available wireless networks. But as far as wireless utilities go, it's pretty weak. It's slow, it doesn't give you any idea about signal strength or quality, and it doesn't give you much information about the security or lack thereof on the available networks. iStumbler, a free application for the Mac takes care of this and provides a much better solution to the above problems. It also can be used to detect Bluetooth and Bonjour networks.