Kismet for Mac OS X (KisMAC)

Kismet is a tool for wireless sniffing (just viewing what’s already passing through the air). And KisMAC is the OSX version. Best part about KisMAC is the Apple Airport Extreme card drivers for both Active and Passive support. Active, meaning you can see but can’t collect, and passive meaning you can see and collect.
So if your on OSX and you want to see the wireless in your area and collectively watch what’s be sent around, getting KisMAC is a good starting place.