Below are the top 3 preparation books for bitsat 2013
Comprehensive Guide to BITSAT (with FREE CD) by Disha Experts
A Complete Success Package for Online BITSAT 2013 by Arihant Experts
BITSAT 2013 Birla Institute of Technology & Science: 12 Practice Papers (With CD) by G.K. Publications
There are other bitsat books which simplify the exam for students.The secret of success is behind the selection of right preparation books.