I noticed you said Cleric was the hardest to work on, and that you have an idea for it. What I like about this system is the options within each character class — that's what was missing from 3.x, IMO. With that in mind: some ideas for cleric options.
The Cleric's major differentiating factor (what separates one from another) has always been spell selection, but that changes daily. What about a tree that is only useful with a certain type of spell, but expands the use of that spell? Something that allows the cleric to channel energy or spell effects into his weapon? A Bard-like ability to stack or expand buff spells?
The ability to Turn has always seemed a little confining to me. Why just Undead? What about a tree like the Ranger's Favored Enemy where the cleric can choose a creature type to which his god is opposed? Even if limited to outsiders and unnaturals (like Undead), the ability to turn (or supplicate) Lawful Outsiders, Evil, Undead, etc., and corresponding bonuses to fighting (or bargaining?) with them could really set each Cleric aside.
A major defining feature of the Cleric is, of course, healing… there's got to be something you can do with that…. Nothing comes to mind, but I'll give it some more thought.
~Joe