How can I view all Wi-Fi network names (SSIDs) in my area? I live in an area dense with Wi-Fi coverage. Eight SSIDs show from my menu bar dropdown, but I know there are more. Where can I view a full list of networks in my area? (I'm on a 2011 MacBook Air running 10.8, but it'd be nice to know in general.)
There is a program you can run in terminal.
/System/Library/PrivateFrameworks/Apple80211.framework/Versions/Current/Resources/airport -s

Update for 2021:  This command still works (as written) in OS 11 Big Sur.