The Ultimate Handbook is an absolutely fabulous website with all kinds of information on Ultimate Frisbee, the greatest sport known to man. It has rules, information on tournaments(still a little skimpy here, visit www.upa.org for better tournament info), suggestions for drills, tips for captains, a history of Ultimate, Ultimate humor, links to other Ultimate sites, and lots of information on health and fitness particularly relevant to Ultimate players. This site is hugely popular among Ultimate players, and is constantly referenced by players, or at least those in my area. There are video and audio tutorials, accurate descriptions of a variety of exercises and drills that teams can use, and advice for captains on how to run a tournament or a team. The Ultimate Handbook is probably the most referenced document in Ultimate, with the possible exception of the rule book, although, to be fair, the Ultimate Handbook contains the rule book. Regardless of whether you have never picked up a frisbee in your life, or whether you've been playing Ultimate for 15 years, you can probably learn something from the Ultimate Handbook.
Oh, and the URL is http://www.ultimatehandbook.com.