Upon reviewing Complete Divine, I noticed the Shugenja class, which appeared to me (again, I'm probably wrong, but it at least appeared) to have a somewhat high number of spells known for a spontaneous casting class.

He has a similar framework to the sorcerer in spells per day (ending with 6 of each level at level 20) and he gets a wide variety of spells known as well. I didn't check his spell list, and that may be the reason, but it seems like it could be a quite powerful class on first inspection? Then again, so do lots I suppose.