There's a hidden room in the Simpson's house that has only been seen in 3 episodes. It's located at the back between the kitchen and the garage.
The show began as an animated short film on the Tracey Ullman show. These episodes are hard to find as only a few of them have come out on the Simpsons DVDs.
The Simpsons has had a huuuuge number of celebrities voicing characters, including Pharrell and Daniel Radcliffe (aka Harry Potter)
There was a Homer, Marge and Lisa in his family. His mum's name, Wiggum, made it into the show with Chief Wiggum and his son Ralph!
Also, Marge's hair was so large because it was hiding huge rabbit ears underneath. Both ideas were scrapped though. Shame!
Homer Simpson answered phone calls live on-air, with real people calling in to ask Homer questions.