What books are best for class 9 Olympiad preparation ?

For Olympiads exposure to questions and solutions of previous year papers is best way. The questions itself will be guide you to read from various sources. For the same, the few HBSCE recommended books are listed below:

1. Indian National Physics Olympiad - Theory Problems and Solutions (2006 – 2009), Vijay A. Singh and Praveen Pathak.

2. Indian National Physics Olympiad - Theory Problems (1998 – 2005), Vijay A. Singh and Shirish R. Pathare.

3. Indian National Chemistry Olympiad - Theory Papers with Solutions (2002-2004), Savita Ladage and Swapna Narvekar.

4. Indian National Chemistry Olympiad - Theory Papers with Solutions (2005-2007), Savita Ladage and Swapna Narvekar.

5. Indian National Biology Olympiad - Theory Papers (2002 – 2004) Compiled by Rekha Vartak, Anupama Ronad

6. Indian National Biology Olympiad - Theory Papers (2005 – 2007) Compiled by Rekha Vartak, Anupama Ronad

7. Question Papers of Indian National Astronomy Olympiad (1999 – 2008), Compiled by: Aniket Sule, Anand Ghaisas and Mayank Vahia.

8. Problem Primer for Olympiads, Author: C R Pranesachar, B J Venkatachala and C S Yogananda

9. Functional Equations, Author: B J Venkatachala

10. Title: Inequalities: An Approach Through Problems, Author: B. J. Venkatachala

11. Challenge and Thrill of Pre-College Mathematics, Author: V Krisnhnamurthy, C R Pranesachar, K N Ranganathan, and B J Venkatachala.

12. Experimental Problems in Chemistry, Savita Ladage, Swapna Narvekar and Indrani Sen.

NSTSE: Advanced problems from RD Sharma, Fundamentals of Physics, Chemistry, Biology (HCV and other authors).
KVPY: Arihant JEE prep books for Physics, Maths and Chemistry. For biology, CBSE Biology books will suffice. In XII standard, you got to choose 3 out of these 4 subjects, so you can choose not to take biology for XII standard KVPY, if you are studying PCM as your subjects. For science and maths JEE preparation material and JEE practice papers are more than enough.

NTSE: Tata McGraw Hill Book for NTSE. The book has two parts: Part MAT (Mental ability test), Part SAT (scholastic ability test). SAT has English, Science, Maths and Social Science. All subject course are that of NCERT syllabus. So it is required to cover the whole syllabus of X beforehand. That requires time. Also CBSE has some optional chapters for Social Science. Hence more time devotion to completing the Social Science section is important, since this is a high scoring part due to the direct answers type questions. Two rounds of Social Science, one round of maths, english and science is sufficient. For MAT section, random practice would suffice.