WotC used to have something similar to this in their Download archives (I think it was a previous submission). They were basically paladins using elemental energy to combat mages at their own game (churches were in charge, and arcane magic was illegal, sort of). they carved runes into their armor to hold spell energy, which they used for a limited number of spells.
It was a single PrC, but progression was based on the element you chose to follow.