If you wish to understand the Cavalier class and to expand the options available to these mounted combatants, the Cavalier’s Creed is an excellent sourcebook. The feats contained within are mostly applicable to all classes but especially those characters with a mounted focus.
The Cavalier’s Creed: Advanced Feats is a 16-page PDF (13-pages if you remove the cover, ad and OGL page) for the Pathfinder RPG written by Sigfried Trent and published by Open Design. This is part of Open Design’s Advance Feats line for Pathfinder.
Sea of Stars RPG Design Journal 