The link above will guide you to the full annotated text at Surlalune. The really really short version: a bunch of animals are about to get killed by their owners so they go to Bremen together and end up scaring off a bunch of robbers and enjoying the loot themselves.
Anyway, a friend of mine lives in Germany and mentioned that she was going to Bremen this summer and I was all excited and she promised to get some pictures for me. So here are the famous animals-donkey, dog, cat, and rooster (in the tale they stand on each other's backs the first time they scare the robbers).
This picture is from wikipedia, which says that it's supposedly good luck to rub the donkey's front legs, which is why they're all shiny.