Book list from Source-1

* Physical Geography - Savinder Singh or A.N. Spahler
* Geomorphology - Strahler and St.'ahler
* Human & Economic Geography - Leong and Morgan;
* Dictionary for Geography - Penguin
* Soil Genesis - Daji
* Geography of India - Dr. Gopal Singh
* Physical Geography made Simple - Richard H. Bryant (Rupa Publication)
* Settlement Geography: Social and Economic Geography made Simple -Rupa Publication
* Political Geography- R.D. Dixit or Manorama Sharma
* Population Geography- R.C. Chandra
* Evolution of Geographical Thought - Sudeepto Adhikari & Majid Hussain
* Climatology - D.S. Lal
* Reading in General Geography and Geography of India - R. C. Sharma
* Physical and Human Geography - Leong
* Urbanisation and Urban System in India - R. Ramchandran
* Oceanography - Sharma & Vattal
* Ecosystem - Odum
* Human Geography - Chandra
* Regional Development and Planning - Chand and Puri (Main)
* Physiography - R.M. Tikka
* Soil - Stroller & Stroller
* General Geography of India (Part II) - N.C.E.R.T.
* Regional Geography of India - N.C.E.R.T.
* Gazetteer of India (Part I)
* Economic & Commercial Geography of India - CB Mamoria or Sharma & Cautiaho
* Economic and Social Geography made simple - R. Knowles and Warning
* Physical Geography in India - C B Pichamuthu
* Cartography - R. C. Singh
* Economic Survey
Acknowledgement: Booklist from source-1 adopted from www.groups.yahoo.com/ias_2003.  Thanks a bunch to Mr.Prakash.

Book list from Source-2

Basic Reading

1.   Strahler, A.N. or Strahler & Strahler : Modern Physical Geography.
2.   NCERT—11th and 12th class Geography books.
3.   Geography Made Simple series by Rupa publications.
4.   Rama Chandran—Urbanization and urban systems in India.
5.   Five Year Plan document.
6.   Yojna/Kurukshetra/Employment News.

Further Reading

1.    Small, R.J.—Study of Landforms.
2.    Eyre—Soil, Vegetation and Climate.
3.    Trewartha, G.T.—An Introduction to Climate.
4.    Sharma & Vatal—Occanography for Geographers.
5.    Adhikari, S.—Fundamentals of Geographical Thought
6.    Dikshit, R.D.—Political Geography
7.    Northern—Urban Geography
8.    Hurst, M.E.—Geography of Economic Behaviour.
9.    Symons or Moryan & Mutton—Agricultural Geography
10.  Leong, G.S. & Morgen—Human & Economic Geography
11.  Sharma & Continho—Economic & Commercial Geography of India
12.  Chand, Mahesh & Puri—Regional Planning in India.
13.  Leong, G.S. Certificate to Physical Geography
14.  Critch field, Elements of Climatology
15.  Singh G., Geography of India