Wargames are computers set up for you or a team to hack (legally). Mainly these games are played to learn more about system penetration and how to prevent those penetrations.
Wargame Links:
http://hax.tor.hu/welcome/
http://www.zeroidentity.org/
http://www.hackerslab.org/
http://www.overthewire.org/
http://www.mod-x.co.uk/
http://www.hackthissite.org/
http://www.rootthisbox.org/
http://www.hellboundhackers.org/
http://hackergames.net/
http://www.honeynet.org/
http://www.trythis0ne.com/
http://intruded.net/
http://chumley.biz/
http://smashthestack.org/
http://www.blind-dice.com/
http://www.net-force.nl/
http://www.bright-shadows.net/
http://www.dareyourmind.net/
http://www.fatetek.net/
http://www.hackits.de/
http://www.hackquest.de/
http://www.rankk.org/
http://fifthcrack.com/