I'll go you one better -- I have, like, the opening four bars of Pinky & The Brain's theme song stuck in my head. I've caught myself randomly humming it these past few days.
Every listening exam/test here use the music "Greensleeves", so it got really stuck into my head. It's sometimes call as the "nightmare music" here because students must listen to it while preparing for the questions.
Not a song but a melody is stuck in my head. Its a melody of a musical doll which is playing almost all the time in the birth-room of my second grand-child, born yesterday !