In all seriousness, Zen of Screaming
Me and my bandmates used this back in the day. She has a pretty impressive list of vocalists she's helped out, both with singing and screaming. Including Kevin Bacon, so you know it's good.
She teaches how to scream/growl without hurting your vocal cords, which helps tons if you want to practice for more than 2 hours straight.http://www.melissacross.com/home.php?