Have Some Fun
Learn to play a game: ChessDryad.com's How to Play Chess page will get you from learning the mechanics of the game to classic moves, with primers and flash animations. Veteran bridge author Richard Pavlicek has put his Bridge Basics textbook online for people wishing to learn the popular card game. For neophyte poker players, Charles Bloom has put up a Texas Hold'em primer.
For sports (or anything else highly physical and visual), you can't beat YouTube: For example, I found dozens of skateboarding how-tos, but the one I actually felt I could learn from was this unpolished but accessible effort credited to one "Eswolowski" and posted by a user named tevens22.
However, not all sports stuff is on YouTube. Aspiring soccer moms and pops should check out How to Play Soccer, which not only teaches the rules of the game, but offers tips for parents who serve as coaches or spectators.
Aspiring musicians, dancers and filmmakers can also find instruction online. SoYouWanna.com offers a guide for making low-budget movies.
Like to sing along in perfect harmony? ChoralWiki maintains a database of free choral sheet music. If your garage band needs help figuring out the guitar solo in Dire Straits' "Sultans of Swing," head to 911tabs, a very nifty search engine for tablatures (musical annotations showing fingerings for specific pop and rock songs). You can search by song and by instrument.
Again, YouTube shines when it comes to teaching a musical instrument. But perhaps the coolest YouTube how-to project for the performing arts is Inez Markeljevic's 40-video tutorial for learning the dance of the zombies in Michael Jackson's classic Thriller video.
Created in hopes of setting a Guinness Book of World Records for the most number of people performing the dance simultaneously around the world (see her site, Thrill The World, for more on this), the video tutorials break the song into sections and then into steps with mnemonic aids to remind you of what you should be doing. I'm already up to section 3!