Other Resources

Backtrack, a Linux pentesting distribution: http://www.backtrack-linux.org/

Fast, with a staggering number of attack frameworks and tools, this is popular and well-maintained.

Use it for an attacking OS - and, with VMWare or Virtualbox's ability to pass-through the host machine's USB devices, you can practice wireless security auditing with a virtual machine.

More exploitation targets: http://lwn.net/Articles/437221/

The linked article has a very good list of target distributions and VMs, along with a short discussion of each.

DVL is another project like Metasploitable: http://www.computerdefense.org/dvl/

DVL hasn't been updated recently, but this seems to be a working mirror of the most recent version (1.5).

Some sites with other useful materials: