Cleric Domain - Arcana or Mysteries

(Originally found on The Chamber of Mazarbul) 

Domain: Arcana OR Mysteries
Choose another spellcasting class.  You can swap out one of your own spells for a spell of your level or lower from that class.  
Adventurer Feat: You can use Wisdom for the swapped spell's attack and damage.
Champion Feat: You can swap out 2 of your own spells for 2 spells of your level or lower from that class.
Epic Feat: You can swap out 3 of your own spells for 3 spells of your level or lower from that class.  Additionally, you can choose a second spellcasting class, and spells you swap out can come from either additional class.
Invocation of Arcana/Mysteries: The crit range of your spells and spells cast by nearby allies expands by +1 this battle.