'size of a cow' by the wonder stuff (ask your dad) actually works! if you 'sing' it in your head, it gets rid of whatever song is currently stuck in your head, and then you're not stuck with 'size of a cow' in your head because it's SO RUBBISH, it doesn't hang around! brilliant. this tip was taught to me by art brut.
i actually liked the song as a nipper so it doesn't ALWAYS work. but anyway. try it sometime.
current earworm: that fryars single.