The Snopes.com "25 Hottest Urban Legends"
I love Snopes. It's my go-to resource when someone forwards me an email and I know it's fake, but I don't have time to type out a response explaining why email forwards are always hoaxes. The folks at Snopes have already done the legwork, in well-researched articles that validate all sorts of hoaxes, urban legends, and crazy internet stuff. Sending someone a Snopes link is the digital equivalent of calling BS.
To make Snopes even better, its authors (the Mikkelsons) actually reply to their email. Last year I wrote an article for mental_floss involving MacGyver, and was using a Snopes article as a source. Being good journalists, they had actually cited their own sources -- but I couldn't find those source articles through my local library system. So I went ahead and emailed the site owners asking if they had tips on finding the articles. To my surprise (and delight) I got a personal response the next day, including PDFs of the articles in question. Now that's awesome.
So I thought I'd point you to a super-useful page on the Snopes site: their 25 Hottest Urban Legends. Among the top hits that have been personally sent to me by family members and friends are a bogus cell phone telemarketing alert, Microsoft/AOL giveaway, and an alleged Facebook virus, though my favorite from the list is Cut Onion Contamination, in which a claim is made that onions are overwhelmingly responsible for food spoilage, and various claims are made about mayonnaise. Just read it, it's complicated.
Another favorite: the Fauxtography page, which determines the authenticity of all kinds of photos circulated online -- including the photo of a woman hand-feeding hummingbirds (true!) shown above. (Photo copyright 2006 Sam & Abigail Alfano)