1. Levi's Big Flip
When Levi's first assumed an alter ego ("Unbuttoned Films") and uploaded a YouTube video  titled "Guys backflip into jeans," it wasn't expecting sky-high exposure. But since its May 2008 debut, the two-minute must-share video -- and its subsequent press coverage -- has helped the denim giant reach an estimated 100 million people.
2. Hershey's Sweet Parties
Hershey's partnered with word-of-mouth marketing firm House Party to let 10,000 people dole out Hershey's new premium Bliss chocolates at sponsored house parties. The soirees lured nearly 150,000 guests, and House Party estimates that they have shared their bliss -- and their Bliss -- 10 million times.
3. HBO's Winning Cocktail
To promote last fall's edgy vampire series True Blood, HBO created fake "Tru:Blood" beverage ads, vampire tolerance PSAs on YouTube, and a seemingly functional vampire-human dating site called LoveBitten.net . The stunts helped True Blood's Sunday night viewership grow 66% over the course of its first season -- faster than The Sopranos did.