This has been done before but I'm a new member and I thought I might ask about this.
There have been a lot of backmasked songs, funnily enough rock.
But that sweet little Britney Spears has done one - Hit me baby one more time comes out as "Sleep With me I'm not too young"
There was one With Ozzy Osbourne which said something like "get your gun"
I tried out Cradle of Filths - Dinner at Deviants palace but it's all a load of gibberish but Led Zep's stairway to heaven, I think it's purposely done, forwards is about heaven backwards hell makes sense.
There a tenacious D one as well which apparently says "Donkey Crap"
There's also the pokemon rap and Eminems "my name is" which forwards as "my name is what etc" backwards it says, "it's slim, It's eminem repeatedly" purposely done? I think so go to http://jeffmilner.com/backmasking.htm for more