Need a little more screen real estate for your MacBook or Windows PC? Air Display, an app that lets you use an iPad as an extension of your computer monitor, solved that problem with its original app.
Need a lot more screen real estate? The new Air Display 2 ($9.99 from Avatron Software) might be worth checking out.
Air Display 2 can be used with up to four iPads as additional monitors.
The iPads work the same as any external monitor, and app windows can be dragged to them at will. A nice feature is that the iPad's touch screen works as expected, effectively adding touch control to OS X if it's connected to a Mac.