I know one of them is taking your wedding ring, putting it on a string and holding it close to your belly. If it swings one way it's supposed to be a boy, and if it swing in another it's a girl. (Can't remember it exactly right now!)
There's another one with mixing your pee with something... chlorox? A blue laundry detergent? Can't remember.
I've heard of lots of ways but can't remember them, If you can please let me know!