One of the guidebooks I really like for D&D 3e is Tome and Blood. The source material is chock full of wizardly goodness, and has a lot of outstanding information for players and Dungeon Masters alike.
Tome and Blood
Tome and Blood: A Guidebook to Wizards and Sorcerers was written by Bruce R. Cordell (who left Wizards of the Coast in 2013 to join Monte Cook’s company) and Skip Williams (a longtime TSR favorite).
The book’s intention is to help players customize their wizards and sorcerers. It includes new magic items, feats, and spells and even introduces new prestige classes (most I’ve never had a chance to role-play).
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