Wireshark (formerly Ethereal) is the world's foremost network protocol analyzer. It has a rich feature set, including deep 802.11 and VoIP analysis.
The latest release (0.99.6) adds full 802.11n dissection and support for the AirPcap-n capture adapter.
It also adds WiMAX and WiMAX MAC-to-MAC (M2M) dissection.