Nexercise has Sworkit Pro (iTunes Link) for the iPhone, iPod Touch, and iPad in the iTunes App Store for FREE (regularly $4.99) for a limited time.

Sworkit takes you through 5-60 minute circuit training workouts requiring no equipment.

Just choose what part of the body to workout and for how long. Options include strength training, cardio, stretching, yoga, and even an option to create custom workouts.