iRwego, a sort-of-cleverly named iPhone app, may not have a very long lifespan, since it's not approved by Nintendo. But I hope it stays—it soundtracks your life as if it were a Mario game.
The idea is to put it in your pocket, and the accelerometer will detect your movements and play the appropriate Mario sound effect. Jump, and it'll make the distinctive Mario jump sound; crouch, and it'll make the "worp worp worp" sound as if you're entering a green pipe. Also included are brick hits and Goomba-stomping, among other noises, tunes and a few choice Mario catchphrases. It's available now (hopefully) for a buck. [CNET]