I just discovered this excellent Web page: Jeff Milner's Backmasking Site. I have no idea who Jeff Milner is, but I applaud him for doing our culture a valuable service. As a kid, I was way into stories of backward messages in records; my friend and I even messed up his parents' turntable trying to hear the "turn me on, dead man" in "Revolution No. 9." Later, at camp, some guys and I figured out how to crack open a cassette tape and switch the reels so that you can play it backward; we spooked ourselves hearing "It's fun to smoke marijuana" in "Another One Bites the Dust." It didn't occur to me at the time that a supposed love of smoking weed was probably the least weird thing about Freddie Mercury.
So enjoy. I think my favorite is "Break on Through." I hate the Doors; I consider Jim Morrison one of the most unintentionally hilarious characters in history, so it's fun to think that maybe, just maybe, he was actually the personification of evil.