Security Challenges and Games

Defcon CtF Prequalification Challenges (http://nopsr.us/ctf2006prequal/) from this year, created by Kenshoto.
Skillz challenges (http://www.ethicalhacker.net/content/category/2/12/2/), hosted at ethicalhacker.net.
Ed Skoudis's movie and TV themed challenges (17 in all) on http://www.counterhack.net/Counter%20Hack/Challenges.html.
Project Webgoat (http://www.owasp.org/index.php/Category:OWASP_WebGoat_Project) from OWASP.
http://www.hackr.org, where several challenges are available at different skill levels.
http://quiz.ngsec.com/ and http://pulltheplug.org/wargames. Both are classics in this genre, worthy of your attention.
www.hackthissite.org, which has a very large collection of hacking challenges and sort-of "real-world" scenarios.
Foundstone's Software Application and Security Services offer a fabulous collection of games and challenges (http://foundstone.com/index.htm?subnav=resources/navigation.htm&subcontent=/resources/s3i_tools.htm)
Welcome to the DEF CON 13 WarDriving Contest
http://www.securitytribe.com/dc13wardrive/index.html
The 2005 UCSB International Capture The Flag
http://www.cs.ucsb.edu/~vigna/CTF/
HITBSecConf2006 - CAPTURE THE FLAG OVERVIEW & RULES
http://conference.hackinthebox.org/hitbsecconf2006kl/?page_id=61
ToorCon 8 - RootWars
http://www.toorcon.org/2006/rootwars.html
OpenInfreno - An Open Source Root War Engine
http://openinfreno.sourceforge.net. This is a very cool engine on which to build CtF games.