Hello, 

The best books for NEST preparation are as follows:

1. For physics

• Concepts of Physics by H.C Verma
• Aptitude Test Problems by S.S Kotov
• Objective Physics by Mahesh Jain
• Practice problems in Physics for Engineering  Examinations by S.Mishra
• Physics for Engineering and Medical Examinations by Ajit Singh Panwar
• Problems in Physics by A.A Pinsky

2. For chemistry

• A Textbook of Organic Chemistry for IITJEE by R.K Gupta
• An objective Approach to Organic Chemistry by R.K Gupta
• Textbook of Chemistry for Class 11th and 12th by NCERT
• IIT Chemistry by O.P Agarwal
• Entrance Chemistry by Bhakta

3. For biology

• Objective Biology by SBiswas & A Biswas
• Textbook of Biology by NCERT
• Elementary Biology for Class 12 by K.N Bhatia
• Biology by S.C Verma
• Biology by A.C Dutta

4. For Mathematics

• Higher Algebra by Hall and Knight
• Problems in Calculus of One Variable by I.A. Maron
• Plane Trigonometry by S.L Loney
• Integral Calculus by Amit M Agarwal

Hope this will help you. Best of luck.