In addition to using the wireless-client, stumbling, and
network analysis software mentioned here, you have some
additional ways to search for wireless devices that don’t
belong ie some basic port-scanning and vulnerability
assessment tools can give you useful results.
Here is a quick list:
2 GFI LANguard
These programs aren’t wireless specific but they may
be able to turn up wireless-device IP addresses and
other vulnerabilities that you wouldn’thave been able
to discover otherwise.