[RPG] Ways for a Sorcerer to cast Spells he doesn’t “know”

dnd-3.5efeatsmagic-itemssorcererspells

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 :).

Best Answer

You're looking for this handbook, aptly titled: "Ways to Expand a Spell List".

With the requirements you stated above:

Magic Item Compendium - Runestaves - Item - allows an arcane caster to expend a slot to cast the spell in the staff

Explorers Handbook - Drake Helm - Item - Can attune spells to the helm; act as if they are on your known-spells list

Also, don't forget summons. Many summons can cast spell-like abilities, which makes your "spells known" a practice in "how well do you know your summon monster list?"

Furthermore, don't underestimate the leadership feat. A level 20 villain can have a level 18 cohort who specializes in arcane geometries and other nuanced spellcasting... and is a prepared spellcaster. If your main villain is the mailman and his "grand vizier" is an archivist or factotum/chameleon, you get a scary evil dude and his crazy-prepared henchman who gets all the work done. The henchman, himself, will have a psion as a cohort, and the psion will have a binder/anima mage as a cohort...