Books recommended for Gate....

MATHS:

B S GREWAL or H K DASS is sufficient. But my personal choice is H K DASS. At the last stage of your preparation u can do your practice from GATE

ENGINEERING MATHEMATICS

by R K KANODIA. It has large collection of objective type question. If u want to study more, u can go through ERWIN  KREYSZIG (WILEY publication)

MANUFACTURING SCIENCE :

In Manufacturing, whether it is GATE or IES 70% questions r numerical based. Amitabh Ghosh is a very good but tough book. It has very limited theoretical part and more numerical part. P N RAO is a good book.

PRODUCTION TECHNOLOGY

by P C SHARMA (S.CHAND publication). Its theoretical part is better than P N Rao. PRODUCTION TECHNOLOGY by R K JAIN (KHANNA publication). It has huge volume of theoretical part.

INDUSTRIAL and OPERATION
RESEARCH:

MAHAJHAN or HEERA Gupta. Numerical from Inventory, PERT/CPM and Queuing are most important.

THERMODYNAMICS

I will prefer P K NAG rather than R K RAJPUT. I know P K NAG is a tough book but if u will go through dat book u will have an excellent command over the subject. This book also has the RAC and IC Engine part that is asked in GATE.

HMT

For this you can refer to R K RAJPUT. For more conceptual refer HOLLMAN or INCOPERA.

SOM-

Either PUNAMIA or S.RAMAMRUTHAM is sufficient. You can also refer TIMOSHENKO & GERE for SOM.

FLUID -

MODI & SETH is better than R K BANSAL. For Fluid 1000 Solved Problem Sigma Series FLUID MECHANICS by K.SUBRAMANYA. This book is only for practice not for
foundation

THEORY OF MACHINE

S.S.RATTAN for Numerical problems

Machine Design :

V B Bhandari is preferred.

MATERIALS SCIENCE &
ENGINEERING:

O P KHANNA is a good book or CALLISTER (WILEY publication).