Worth 1000 contests always fascinate me, so Worth 1000 + Muppets (most of them are Muppets, anyway, but you'll also find Wallace, Chucky and Alf) = pretty sweet. This particular contest asked Photoshoppers to stick puppets in unlikely situations. The one above is by taltieri is probably my favorite, but Animal in 300 and Bert and Ernie in 3:10 to Yuma are pretty awesome too. The Kermit and Miss Piggy entry is just... disturbing.
Link to the whole gallery
Kermit's bicycle riding scene in the very first movie is a good exception, but that rule should otherwise never be violated.