Again, the best thing to do is come see some of the crazy things people in our club (or the club nearest you) have been working on. Generally they'll be happy to explain new tricks to you. Going to a club (or teaching someone else to juggle) is also the only way you'll learn multi-person juggling (like club passing). Another fun way to improve your juggling is to go to a festival. Festivals come in great variety, from large international conventions to small one-day events put on by local clubs. Wherever you go you're likely to find friendly and enthusiastic people to juggle with. Follow this link for a schedule of upcoming festivals.
The best place on the net to start looking for help is the Juggling Information Service. In addition to a help section, the JIS also has a searchable full-text archive of back issues of Juggler's World, a searchable archive of the newsgroup rec.juggling, and contacts for vendors who can sell you books and videos.
If you're looking for books, there are two books by Charlie Dancey that are particlarly recommended: the Compendium of Club Juggling and the Encyclopedia of Ball Juggling are both very well written and illustrated, and are both packed with ideas. (Here's one place you can order them from.) Dave Finnegan's The Complete Juggler, though not as in depth or as much fun to read, also has some good stuff in it, and covers diabolos, devil-sticks and other props as well as balls, clubs, and rings.