Calibration Box
Sometimes, you just need a box.
Notes
First off, this is 100% taken from Unity3D's own calibration scene, i've just stripped out all of the other scene junk and whittled it down to just the box.
How to use
Download the latest release and import it into your Unity3D project. From there you just need to drag the Calibration Box prefab out of the Project tab and into your Hierachy or Scene view.