What is the maximum paragon level?

Solution 1:

The wiki states that since the release of Reaper of Souls (Paragon 2.0):

There is no cap on Paragon levels. Players can now earn as many Paragon levels as they please. All that needs to be done is to simply fight monsters and complete quests with a hero already at lv. 60 or 70, depending upon the player's (lack of, if appropriate) access to Reaper of Souls.

This chart (provided by Arperum) shows a current XP requirement per level, up to 2000. (I would post it here but it would be way too huge)

As for a fancy pie chart, I can only provide (an old model) up to 100, as the 2.0 version suggests there is no level cap.