interesting tidbits;
in the song "empty spaces" on pink floyds 'the wall' the phrase "Congratulations. You've just discovered the secret message. Please send your answer to Old Pink, care of the funny farm, Chalfont." is recorded backwards near the end (and its very faint so listen carefully)
in the song 'darling nikki' by prince there is a message about the 'lord coming home' recorded backwards at the end..
....and.... these two are the only ones i can think of right off hand....