As everyone knows, Ioun stones rule.
They come from the Jack Vance Dying Earth series, where the insane mages (and everyone in his world is fucking crazy) sort of use them as a measure of wealth. Like many other items (Iron Bands of Bilarro) and spells (The Excellent Prismatic Spray, Imprisonment / Freedom, etc.) in his world, along with his spell memorization scheme, they were imported wholesale into early D&D.
So this dude got a compilation going.
http://d20.jonnydigital.com/2008/09/iou ... lete-guide
