"These were volumes compiled by many wizards of the past, untidy folios collected by the Sage, leather-bound librams setting forth the syllables of a hundred powerful spells, so cogent that Turjan's brain could know but four at a time.....He stared down at the characters and they burned with an urgent power, pressing off the page as if frantic to leave the dark solitude of the book."
--The Dying Earth, Jack Vance
....or, as Jeff Rients put it
"Spells are almost alive with power. Memorizing a spell is kinda like putting a demon in your head."
Wizards are highly-skilled professionals--the networks of neurons and myelin in their skulls have been trained throughout years of apprenticeship to grow and branch into bizarre knotted geometries capable of encasing and enclosing unnatural forces. The bio-mystical energies needed to bind dweomers to the earthly plane have been known to persist in the minds of magic-user eons after death.
So, naturally, while spellbooks are all fine and good, what your real heavy-type avant-garde alchemonecromancer wants to get his or her hooks on is brains. Wizard brains, mostly. The hardest-core work in the field is digging up long-dead sorcerer-kings of ages past to extract the formulae for long-lost spells of the oldest schools (like, say, sleep from before it got a saving throw) but fresh brains have their uses as well.
Some uses for the brains of dead wizards:
-It is possible to "read" the spells remaining inside a dead caster's brain in order to copy the spells into a spellbook or onto a scroll. The ritual can be learned by a necromancer at 4rd level, by an alchemist at 2nd level, and by any other arcane spell-caster at 5th level for an x.p. cost equal to 1/5th of the x.p. required to reach the next level in whatever system you're using. This can only be done on a full moon at the end of day upon which the mage performing the ritual has shed no blood.
-Any alchemist of 3rd level or higher can "pulp" the brain--that is, use the brain to create a potion capable of replicating the effects of whatever spells were left in the caster's mind at the time of death. However, if the brain has not been "read" first, there is no way of separating one effect from the other, so the prepared potion will simultaneously produce effects matching all the spells contained int he arcane brain.
-The proper application of embalming fluids and electricity to a brain can cause it to release any spell memorized but uncast at the time of death. The secrets of this process may be learned by any arcane spellcaster at level 7 for a cost of 1/3rd of the x.p. required to reach the next level of experience in whatever system you're using (alchemists can learn it at 3rd level for the same relative price). The mage will have to supply his or her own electricity. There is no limit to the level of the spell that can be "liberated" by this means, but setting loose a spell higher than the caster's level results has a 10% cumulative chance per level above the caster's allowed casting level of causing the spell to misfire (or overfire) in some entertaining way.
-Certain kinds of rune-etched brass golems can be powered using the brain of a deceased spellcaster as a sort of battery. These golems can cast whatever spells were left in the brain at the time of the caster's death. They can also be "recharged" with new brains at any time. (Enn-Zinn the Undecipherable has been discreetly harvesting the minds of sorcerers via a network of assassin-nightengales for forty years in hopes of one day powering an unstoppable army of brass golems kept in a chamber deep beneath the Red Palace of Emperor Claw is what they tell me. But, y'know, they say a lot of things, so whatever.)
A blue dragon can cast (some say "only cast") spells contained within any brain they've eaten.
High level sorcerer brains (15th level+) are so steeped in occult and space-folding mathematical sciences that they can actually be used to trap demons. The minimum level of the brain required to do this is 15 + (HD of demon to be trapped).
Yes, that's a Reaper Miniature and, yes, they sponsor our TV show. If you spent your days getting boxes of free miniatures all the time you'd probably start to like some of them, too.