A Wizard prepares and casts Spells from his Spellbook and can therefore cast pretty much any Spell he has the appropriate Slot for and can get a Scroll to learn it from.
I'd like to have a similar Method for a sorcerer. Say you have a 20th LVL Sorcerer building his Magic castle ( or Vila or...) and he needs to spend cash on every single protection Spell and unseen servant he wants to place... that's just plain stupid. So help my villain be self sufficient :)!
So I want a way for a sorcerer to expand his casting choices in a significant way.
The methods shouldn't involve a cost associated with each use. like buying scrolls, or using (limited) wish. An investment the character needs to do once is ok (such as an item to add additional Spells known). Increases in casting times are fine. Increased costs in resetting resources, like spell slots or 1/day abilities are fine. I'm mostly looking for feats or items, but PrC's like mage of the arcane order are ok as an option, though I'd prefer possibilities not interfering with the Classes of a build. The villain doesn't exist yet, so there aren't any more specific requirements :).