HackThisSite.org

I just found a site called w*w.hackthissite.org. its really great. you all should check it out

Hack This Site gives aspiring computer users a legal environment in which to test and expand their hacking skills. Put your skills to the test in a series of hacking challenges, including basic web hacking, realistic web missions, application hacking, and encryption contests. Get informed with user-submitted articles, external resources, and political activism. Get involved with the HTS newsletter. Communicate with other members in the forums or the IRC server.

One of the things that may have caught your eye was the "application hacking". You download a file and you have to find out the serial, using many tactics, getting harder by level. I got thru level 2 just a minute ago. no problem! and i have minimal knowlegde of cracking.
I'd be curious to see how good you all are, and maybe test your own knowledge.
But as said, this site is good for all types of hacking. Have fun!