Zephyr, by jailbreak phenom chpwn, brings iPad-style multitasking gestures to the iPhone.
From swiping up to show the multitasking switcher or quickly swiping to a different app, Zephyr is all you need to quickly and easily control multitasking.
Zephyr registers bezel-to-screen swipes, which makes sense given the smaller surface area of the 3.5-inch iPhone vs. 9.7 inch iPad display. While only the 2 gestures listed above are currently supported, anyone already familiar with their iPad counterparts will realize the efficiency boost they can provide.
If you're jailbroken, you can grab it now from Cydia for $2.99.