1. Mohit Bhattacharya- (New Horizons Of Public Administration )
2. M.Laxmikanth <-- don't go xerox here - buy original.
3. Nicholas Henry (Public Affairs and Public Administration ) <-- only some chapters are imp so you can go xeroxing.
4. 
   
   
   Stephen Robins : Essentials in Organizational Behavior (Low Price Edition)
   1. There are two Stephen Robbin books in the market, one is thick like encyclopedia but you've to buy the thinner book –which is only 300 pages.
5. Prasad & Prasad (Administrative thinkers) OR TMH/S.R.Maheshwari (most people use Prasad & Prasad.)
6. Avasthi & Avasthi (Indian Administration)<- MUST, because this covers entire Paper-2 syllabus. OR Arora & Goyal (not recommended cause its not updated)
7. Wizard Indian Polity .
8. 
   
   
   Solved prelim Paper set of Public Administration Prelim
   1. (Arihant / Wizard) –

don't buy the yearwise paperset (i.e. 2001,2002,...)

but buy Topic wise arranged papersets (like Arihant / Wizard etc) which gives you answers + detailed explaination as well, so you can see what UPSC asks from each topics and why is the given answer the correct answer.

Optionally

1. Avasthi & Maheshwari (you'll notice that some chapters of it are copy paste of Avasthi & Avasthi.)

Don't buy Sharma Sadana (its just one thick boring book– but if you do A& M then no need to go for S& S )

Instead of A&M, you use Fadia And Fadia (same things, but I like A&M. for no rational reason.)

If you've been reading list of books from other websites / coaching classes.

Then you'll see that they've recommended

1. LM Prasad
2. OG Glen Stahl
3. Terry & Franklin
4. Nigro & Nigro
5. IIPA Journals.

All these are good books but I did not use them cause

1. Lack of time
2. I can't find them in the book stores where I live. 
3. They're more about MBA and less about Public Administration
4. I did not see many questions in UPSC that my books did not cover and these books did. i.e. you might get 1 or 2 questions from them, but for that you've to read and revise 1000+ pages. Its not worth it with respect to, Cost benefit ratio. 

However if you read these books - its well and good but if you can't due to lack of time, then don't worry much.

Apart from that – most importantly,

don't even waste your time glancing over coaching classes etc stuff or even listening to people who talk about it. because more you listen - more your brain starts doubting about your method of preparation. .