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.