If you're trying to polish your hacking skills, here's a list of hacking wargames to try:
Over the wire: http://www.overthewire.org/wargames/
The wargames offered by the OverTheWire community can help you to learn and practice security concepts in the form of fun-filled games.
HackerGames: http://www.hackergames.net/
Within you'll find a comprehensive list of hacking and security related challenges, hackits, wargames, tools, and tutorials, along with user reviews.
HackThisSite: http://www.hackthissite.org/
Hack This Site is a free, safe and legal training ground for hackers to test and expand their hacking skills. More than just another hacker wargames site, we are a living, breathing community with many active projects in development, with a vast selection of hacking articles and a huge forum where users can discuss hacking, network security, and just about everything. Tune in to the hacker underground and get involved with the project.
Try2Hack: http://www.try2hack.nl/
This site provides several security-oriented challenges for your entertainment. It is actually one of the oldest challenge sites still around :)
Roothack: http://www.roothack.org/
Roothack is a place for computer security related people to experiment with their knowledge, learn new things and hopefully have a good time. The idea is to give information security enthusiasts a place to test new measures of security in a live hacking environment, while at the same time providing a legal place for hackers to attempt to compromise various means of security.
SmashTheStack: http://www.smashthestack.org/
SmashTheStack is proud to announce AMATERIA, a wargame created by kaliman. Some of you may remember this game as "lolwargame" a name that was used during a beta period while it was hosted elsewhere. It has some tasty treats for all you intermediate and advanced wargamers. So everybody give it a try and make amateria feel welcome at her new home.