Links
CTFwS Carnegie Mellon's Capture the Flag with Stuff. Includes rules, pictures and some non-CTF ephemera. (CTFwS has been updated by some other group, too).
US Scouts CTF The US Scouts website has the "traditional" rules, dating from the 1947 Scoutmaster's Handbook, as well as several new ideas.
Carleton's Robo-CTF Project Carleton University's engineering project for fourth year students features "Autonomous Mobile Robots Playing Capture The Flag."
Stanford Quad's CTF Rules If you're ever at Stanford...