Would this help at all?

http://www.csc.liv.ac.uk/~greg/sshdfilter/

Edit: I realize that this is for mac osX, I didnt know if you guys were refering to Mac or PC

insecure.org
has a wide variety of network tools that professionals like myself use for everyday security and pen testing.

NMap or (Networkmapper) is a great tool for learning and testing.
Learning Cisco has helped me alot, by that I mean Cisco courses like the CCNA, CCNP and so on. Depending on what you want to specialize in like wirelss, security, netowrking, or Voip.

I would also run rootkit revealer from microsoft, I found a keylogger that was completely undetectable under Norton corporate, spybot S&D, Adawarepro! rootkit revealer found it then I just removed it under safemode by deleting the files found in the windows/system32 folder and also deleting the registry entry's it made.

With there recent purchase of Ironport they have stepped up there arsonal of network security by ten fold. I recently was able to attend a demo on the Ironport and was very impressed with there product. My company is now using a largescale Ironport as a virusgateway and email scanner and it's working very well.

I have found the senao cd2511 to be very nice for range and acceptance of peek.dll for promiscous mode usage. and cheaply found on ebay