Heirophant is a very good choice. Full progression of caster level (but no progression of spell slots or spells available - not that it matters at epic levels for a cleric, as a cleric doesn't get more spell slots nor more spells known at epic without feats anyway - and no turning increases). However, it's only a five level PrC, so after that you will need to pick up something else - Loremaster is a decent choice, although you may need to burn a feat that is unlikely to help you much to get it.
As for Epic feats - well, depends on the flavor of your character, and what you want to focus on - Leadership (and it's epic counterpart) are sometimes handy (and can be particularly effective if you go with Epic Spellcasting - many might say "broken"). Planar Turning can be useful, although not as much so if you don't keep up your turning level (really fun to Command outsiders that your wizard friend brings up with Planar Binding - pets with Greater Teleport and/or Plane Shift as Spell-like at will abilities can be handy). Bonus Domain can also be very useful, as can the later Spontaneous Domain. If you concentrate hard on Improved Spell Capacity, you can (eventually) take Innate Spell (Tome and Blood) for Miracle (spell-like ability to cast miracle at will).
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