LOL Cats and I Can Has Cheezburger caught lightning in a bottle and went viral. In case you haven't seen it, LOL Cats involves pictures of cats with added captions done in a language developed by the LOL Cats owner. Check out the video above to hear G4's history of the phenomenon.
The success of LOL Cats has launched a bunch of other similar spinoffs. Many have tried to replicate the ubiquity of LOL Cats, including me, but only a few have hit a home run. Upsidedown Dogs has a shot. These are outrageously funny pics of dogs laying on their backs, with their jowls hanging and teeth exposed. The site is a riot--a huge, time-sucking riot.