"Mr Peebles, the world's smallest short-haired domestic cat, measures just 6.1in - the size of a typical sixmonthold kitten. After being rescued from a house where he was badly treated, he lives in a vet's clinic in the U.S."
"Tiny Tim is a 0.75in Roborovski - the world's smallest breed of domestic hamster. The Mongolian mammals were imported to Britain by London Zoo in the Sixties, and they are never more than 2in."
Fairly old article I found when reading cracked.