Pyrit

http://code.google.com/p/pyrit/

Pyrit takes a step ahead in attacking WPA-PSK and WPA2-PSK,
the protocol that today de-facto protects public WIFI-airspace. The
project's goal is to estimate the real-world security provided by these
protocols. Pyrit does not provide binary files or wordlists and does
not encourage anyone to participate or engage in any harmful activity. This is a research project, not a cracking tool.

Pyrit's implementation allows to create massive databases,
pre-computing part of the WPA/WPA2-PSK authentication phase in a
space-time-tradeoff. The performance gain for real-world-attacks is in
the range of three orders of magnitude which urges for re-consideration
of the protocol's security. Exploiting the computational power of GPUs,
Pyrit is currently by far the most powerful attack against one of the world's most used security-protocols.