I believe that what you turn into as an Animagus reflects your personality - the best example, perhaps, being Wormtail (Peter Pettigrew). He turned into a rat, and look at how he turned out. He betrayed his best friends, Lily and James Potter, by selling them to Voldemort. Sirius turns into a dog, which reflects his slightly gruff, very caring, loyal nature. James Potter turned into a stag, but I don't know anything about that. McGonagall can make herself a cat, which are clever and cunning like her. Rita Skeeter, the Daily Prophet reporter, turned into a beetle so that she could "bug" people for information for her tabloid-like articles.

JKR has stated that Harry will not become an Animagus, but she never said anything about Ron or Hermione. If they become Animagi, what will they become? My theories:

Hermione: Well, we know that Hermione is kind and extremely clever…so maybe she could be a cat…or perhaps a wise old owl?

Ron: Ron's got all those brothers to compete with, so maybe he'd be something that really stands out…I've no idea what, though. (Caroline )