IPnetsentryX
Firewall and intrusion detector for Mac OS X includes Ethernet bridging, AirPort configuration, detailed logging and bandwidth accounting.
Little Snitch
Application supervisor for OS X watches all running apps and brings up alerts when a connection is attempted.
MacAnalysis
Security system for Mac OS X actually hacks into the user's server (Unix, NT, Mac) like any experienced hacker would to reveal vulnerabilities.
SecureMac.com
Devotes itself to the security of Macintosh computers, programs and servers.
VisualRoute
Features detailed information about IP addresses and website owners to trace hackers and spammers.