Saraswati, for u I have mentioned below some good books for Geography Main Exam separately for paper-I and Paper-II. Apart some other geography books have also been mentioned that can help u in preparing for civil service examination. 

For Paper - I

Physical geography - Savinder Singh

The Earth’s dynamic surface - K. Sidhartha

Physical geography - Strahler & Strahler

Climatology - D.S. Lal

Physical geography made simple - Rupa

Oceanography - Sharma & Vital

Biogeography - Savinder Singh

Evolution of geographical thoughts - Majid Hussain and Adhikari

Economic geography - K. Sidhartha

Economic and social geography made simple - Rupa

Urban geography - K. Sidhartha

Human geography - Majid Hussain

Geography of population - R.C. Chandra

Regional Planning in India - hand & Puri

Political geography - Dixit

For Paper - II

Physical environment - NCERT

NCERT Class XII

India: Physical aspects - K Sidhartha

Geography of India - Mamoria

Agricultural geography - Majid Hussain

Agricultural problems in India - Sadhu and Singh

Economic & Commercial geography of India - Mamoria

India’s urbanisation and urban systems - R. Ramachandran

Regional planning in India - Chand and Puri

Political geography - Dixit

India: political aspects - K. Sidhartha

Geography

Indian geography - Rammorthy Gopalakrishnan

Physical geography of India - S.M. Mathur

General geography - NCERT

Mineral of India