What's the overall character theme?
If you're trying to be a healer with RSoP (which is certainly the prestige class to do it, my word), Combat Medic from HoB is good, as is Paragnostic Apostle for... some things....
If you're not bound by setting, Sovereign Speaker makes me happy, but ymmv.
If your DM allows you to take a feat to cheese the requirements, Dweomerkeeper is awesome if you don't mind the BAB hit; Mantle of Spells is really what you make of it.
If you don't mind losing 1 CL, nine levels of Mythic Exemplar as an exemplar of Imdastri is not bad; +4 Saves, 1-2 Luck Rerolls, Immediate action immunity to Mind Affecting. It's not super great, but not bad either. If you don't mind the second CL loss, the Capstone is pretty cool; +2 Wis, and spontaneous casting from the Luck, Strength, and Protection domains.
Monk dip to enter Sacred Fist? If your DM rules that the text trumps the table, you get epic bonuses.
This is all very general advice; define "improves".