Here is a list of Fluid Power books, I have collected over the years, to add to Peter's offering.
"Fluid Power Design Handbook," by Frank Yeaple
"Fluid Power Technology" by Don Norvelle
"Fluid Power Theory and Application" by James Sullivan
"Power Hydraulics" by Miachel J. Pinches & John G.Ashby
"Principles of Hydraulic System Design" by Peter J.Chapple
"Fluid Power Systems and Circuits" by Russ Henke
"Fluid Power Maintenance Basics and Trouble Shooting by Richard J. Mitchell and John J. Pippenger
"Basics for the Fluid Power Mechanic" by John J. Pippenger and Greg Gordon
"Zero Downtime Pneumatics" by Dr. Z.J. Lansky P.E. and John J.Pippenger P.E.
"Fluid Power the Hidden Giant by John J. Pippenger,P.E.
"Fundamentals of Fluid Power" by William D. Wolansky,John Nagahosian & Russel W. Henke
"Basic Fluid Power" by Dudley A. Pease & John J' Pippenger
"Designing Basic Pneumatic Control Circuits by Bruce McCord
"Hydraulics" by Deere & Company
"Trouble Shooting Hydraulic Circuits" by Rory McLaren
"Industrial Hydralic Contols" by Peter Rohner
"Industrial Fluid Power Vol's. 1,2 & 3 by Womack Machine Supply Co.
"Fluid Dynamics" by W.F. Hughes & J.A. Brighton
"YourGuide to the Electronic Control of Fluid Power
by the National Fluid Power Association
"Pneumatics and Hydraulics by Henry L. Stewart
"Hydraulic Cartridge Valve Technology: by John J. Pippenger
"Electronically Controlled Proportional Valves" by Michael J.Tonyan
"Industrial Hydraulic Systems" by D.D. Banks & D.S. Banks
"Zero Downtime Hydraulics by John J. Pippenger
Bud Trinkel, Fluid Power Consultant