There are a number of NUM keys that show in a 'perfect view'. After pressing one how do I go back?
There is an addon for that™
Stored Views is bundled with blender 2.79. Simply open up the user preferences and enable Stored Views.
Now in the 3D view go to the properties region ( N ) and click the Initialize button under the Store Views panel (it's probably at the bottom).
Now you can save custom views and go back to them at any time (still no undo support though). Start by clicking the Save Current button, you will now have something that looks like this:
Granted with just one stored view its not to useful. However I labeled the impotent buttons. The Cube button outlined in red is the button to switch to that view. The blue line is highlighting the Save Current button which is used to store the current view.
A normal looking screenshot with more views saved:
The triangle on the indented line is indicating that the 3D view is in the same position as that view. (That feature breaks when using multiple 3D views)