If you've ever thought about using your iPad as an extra monitor alongside your main computer screen, check out this very useful app from Avatron Software, which is designed to help you do that very thing. It's called Air Display, and costs $9.99 from the iTunes App Store. They say it's compatible with both iPhone and iPad, but I would think that it's much more suited to the iPad's larger screen, see how you get on with it though!
To start using your iPad as a second monitor, all you have to do is install the app, then place your iPad next to your computer. The app works via Wi-Fi and uses the iPad's auto-rotation facility, and has a screen refresh rate of 150 frames per second.
Currently Air Display only works with Macs, with Avatron suggesting that it works best with the MacBook Air and MacBook, and they also say that it's a good idea to use a stand as well, so that your iPad is placed in the optimum position. They are currently working on a Windows version for all you PC users out there.