See : BOOKS FOR PRELIMS
To gain knowledge on diverse topics it is prudent to read standard texts rather than depending on materials provided by various coaching institutions. First hand reading of basic books enables aspirant to tackle questions of different dimensions.
Reading newspaper everyday is sine qua non of UPSC preparation. A fortnightly magazine like Frontline is a must to enhance understanding about current events related to India and abroad. If possible, also go through The Economist magazine to understand international events.
Following is the list of books that are necessary for UPSC Civil Services Mains exam (links are given to Flipkart which provides nearly 40% – 50% discount on each book and it has home delivery facility to every corner in India- Of course you can buy from nearest shop if that is comfortable and affordable!):
1) Shorter Constitution Of India (Set of 2 Volumes) 14th Editon – D.D.Basu (THIS IS PURELY FOR REFERENCE – VERY GOOD BOOK TO HAVE)
OR This Small Book : Introduction to the Constitution of India 20 Edition or
From Plassey to Partition – A History Of Modern India (Now Super Hit With Aspirants – Choice is yours! )
Available on Amazon India
(read reviews on Flipkart - but not available.)
Or Buy this Imported Vesrion updated with in-depth chapters on Arab Spring and 2008 Financial Crisis: Mastering Modern World History -5th Edition, Norman Lowe
Or this book from Government of India: The Gazetteer of India: History and Culture Vol II
17) History of the World from the Late Nineteenth to the Early Twenty First Century – Arjun Dev (As Norman Lowe is not available anywhere, This is the best book available that covers all the topics)
Other Books Civil Services Aspirants Must Read (DURING LEISURE):
Of course you need to read NCERT texts as well. The above list is for reference and reading as well. As you have plenty of time for Mains, you can savour these books leisurely.
Don’t forget: The Hindu is the mother of Mains preparation now. Cut and Paste every article related to syllabus from October 2012 to November 2013!