I constantly refer to the following books

Tim Rudman - toning
Eddie Ephrams - creative elements, and gradient light.
Fred Picker Notes - I have all of them
The Focal Encyclopedia of Photography
The Darkroom Cookbook- Steve Anchell
The Compact Photo Lab Index
The Print - Adams
The Film Developing Cookbook - Anchell Troop
Darkroom2 - Lustrum Press
The Permanance and Care of Photographs -Wilhelm and Brower
Outline for Pt Palladium - Dick Arentz
History and Practice of Platinum Printing - Luis Nadeau

a heavy dose of the Kodak Manuals