Your Music library:
Pick any song in your music library and make it sound like the opposite sex is singing it. For example, hear what it sounds like when a man sings a Katy Perry song.
If you are a girl, change your voice into a man's. If you're a man, make your voice sound like a girl or make it deeper. You can also speed up or slow down the playback of your recordings giving you the chipmunk or slurred voice effect.