hey aspirant,

if you are referring to GATE ECE Prep, then here are a few books you can refer to, that will serve you the purpose in sastra university or any other univerties to:

1. NETWORKS: As questions from this are mostly in the form of problems, you have to practice lot of exercise problems. For theory you can follow Hayt & Kimmerely or M.E.Van Valkenberg. For problems you should try to solve schaum series and previous years questions of GATE & IES
2. ELECTRONIC DEVICES & ANALOG: Read Microelectronic circuits by Sedra and Smith. This is the best book for learning tough things in a easy way. If anyone is afraid to understand electronics basics than give one reading of Basic electronics and Linear Circuits by N.N.Bharghava, D.C. Kulshrestha which will make your life easier in electronics.
3. DIGITAL: Ronald J Tocci is the best book for easy understanding digital electronics. For microprocessor stuff read instruction set and memory mapping from Ramesh s Goankar. Don't read full text of goankar. See previous year question papers and check from which topics questions are being asked frequently and concentrate on these topics only.
4. SIGNALS: Read theory from anyone textbook like oppenheim or B.P.lathi. As the questions will be mostly problematic so practice previous GATE and IES questions. Write all the formulas of signals at one place in 4-5 pages and revise them everyday morning.
5. CONTROLS: Read B.C.Kuo. This is the best book.Generally questions from controls is straight forward.Solve previous GATE & IES questions.
6. COMMUNICATION: Read B.P.Lathi for Analog Communication part and Shamshanmugam for Digital Communication part. In these days most of the questions are asked on probability. Read Introduction to Probability by Tsitsikilis and Bertsekas.This is best book on probability.If you don't have time to read this book atleast try to solve worked examples from this book because during the last years i have seen good number of questions from this text book directly in GATE on probability.
7. ELECTROMAGNETICS: Read Hayt till Electromagnetic wave equations. For EM wave equation and antennas read Jordan & Balmain. For transmission lines read John.D.Ryder.

For MATHS, APTITUDE and ENGLISH any material in the market will do the job

hope this helps you and let us know if you need more..

all the best!