Santa's Little Helper
The slow greyhound that saved the Simpsons Christmas. Bart and Homer found him at the dog races after he had been kicked away by his owner for being too slow. The dog has had many exciting adventures including running away from home and becoming one of Mr. Burns' guard dog. Bart once took him to school for show and tell, which caused havoc and ended up losing Principal Skinner his job. Bart often calls the dog his best friend.
That big elephant. Bart entered a radio contest and got to choose between cash and an elephant. To the stations surprise, he chose the elephant and they ended up getting him one. Stampy caused many problems in the neighborhood and Bart had to get rid of him.
Other pets include:
Bolivian Tree Lizards
There is also the family cat, Snowball 2. They did have a Snowball but it got run down. Snowball 2 is the replacement. This is actually referred to as Lisa's pet though.