After hopelessly looking for and asking people about my house's stud finder, I gave in and treated myself to this for Christmas: the magic stud finder. I somehow got mine new for $6, must've been on ebay. It really seems like magic compared to the electric kind we had before, that would always stop working if you accidently took it a half a millimeter away from the surface of the wall or would just be beeping and you wouldn't be sure if you found a stud or you found the electrical wiring jackpot. The magic stud finder works with three really strong magnets that you rub all around the wall and eventually they'll stick to a nail in a stud, and bam, there's your stud!
It's not magic, it's just plain ol' science! And I'm crazy about it! No batteries required!