Avatron Software, Inc. has Air Display 3 for the iPhone and iPod Touch in the iTunes App Store for $4.99 (regularly $14.99) for a limited time.

Air Display 3 turns your iOS screen into a wireless (or USB!) display for your Mac.

Increase your productivity with extra screen real estate or mirror your Mac computer display to your iOS device. (Sorry Windows users, this is just for Mac.)

Now with Air Display 3 you can also connect via USB for buttery smooth graphics performance.