The Study Material and Books for GATE ECE students are below.

Linear Algebra, Numerical Methods,Transform Theory Study Material and Books:
Higher Engineering Mathematics by B.S.Grewal
Calculus, Differential equations, Complex variables Study Material and Books:
Intermediate Mathematics, S.chand publications by B.V.Sastry , K.Venkateswarlu ( if i remember ) both the volumes.

Probability and Statistics Study Material and Books:
Probability , statistics and queuing theory by S.C.Gupta & V.K.Kapoor
Networks: Network graphs Study Material and Books:
Network Analysis by Van Valkenburg
Network Theory by Alexander Sadiku, UA Bakshi
Network Theory by Shaum’s outline, Robbins and Miller
Electronic Devices Study Material and Books:
Electronic Devices and Circuits by Boylestead
Solid State Electronic Devices by Benjamin G Streetman
Integrated electronics by Milman Halkias
Electronic Devices and Circuits by David A Bell
Integrated Circuits: Sedra Smith, K.R. Botkar
Electronic Principals by Malvino
Analog and Digital Circuits Study Material and Books:
Engineering Circuit Analysis Hayt & Kemmerly
Electric Circuits by Joseph A. Edminister
Fundamentals of Electric Circuits – Sadiku
Electronic Circuit Analysis by Donald Neamen
Electronic Devices and Circuits by Boylestead
Micro Electronic Circuits by Sedra & Smith
Digital Circuits Anand Kumar, Morris Mano
Signals and Systems Study Material and Books:
Signals and System by Oppenham and Schiener
Signals and System: by Schaum Series, Willsky & Nacob
Signals and System by Sanjay Sharma
Control Systems Study Material and Books:
Control Systems by Ogatta,Kuo
Linear Control Systems by B.S Manke.
Communications Study Material and Books:
Communication Systems by Simon Haykin
Principle of Communication System by B. P. Lathi
Principle of Communication System by Taub & Schilling
Communication Systems by Carlson
Communication Systems by Sanjay Sharma
Electromagnetics Study Material and Books:
Electromagnetic Waves & Radiating Systems by Hayt, JD Kraus
Elements of Electromagneticsby Sadiku
Electromagnetics by J.D.Kraus
Engineering Applications of Electromagnetic Theory by Liao
Few other useful books for GATE ECE preparation.
Gate 2010 by R.S. Kanodia (for questions only)
Previous GATE Question papers(Made Easy Publishers,GK publishers etc)
Previous Engg Services question papers(Made Easy Publishers)
Aptitude Test-D R Choudhary
GATE Physics Self Study Book by Surekha Tomar
Multiple Choice Questions with Explainatory Answers by UPKAR Publication , Agra
Free Video Courses for GATE ECE preparation  by IIT Professors.
Wish you all a great luck with your GATE preparation and wish you the best in results.