OmniPeek Personal is a free version of the commercial protocol analyzer AiroPeek and EtherPeek, with support for both wired and wireless (802.11) traffic. Additional plug-ins may also be downloaded, such as: a Google Maps plugin which plots the location of an IP in Google Maps, a SQLite plug-in which can store packets in SQLite files so they can be searched with SQL queries, and a Remote TCPDump plug-in which can securely (SSH) connect to any Unix or Linux computer (e.g. Check Points FireWall-1) and stream the packets back into OmniPeek for analysis -- all with out having to install any software on the remote end.
