I read somewhere that there's a new word for songs that get stuck in people's heads: earworms. (I hate to think why -- I've always suspected that the term comes from those gross things in the Star Trek movies that crawl into people's ears and take over.) I'll bet there's a scientific reason that particular melodies get stuck and not others, because many people agree on which songs are earworms and which aren't; how many of us have the Habanera from Carmen get stuck, as opposed to M-I-C-K-E-Y M-O-U-S-E? 
To me, the number 1 earworm of all time, even worse than the Mickey Mouse theme, is another Disney number, "It's a small world." Go through Disneyland on the 7-minute boat ride and you'll be singing it for the rest of the day.
Audrey, the Phantom Phanatic, who nonetheless would rather be Jean Valjean, who knew how to make lemonade out of lemons.