I am a second-year B.Tech. student. I want to crack the CAT and get into IIMs. What are some good books with which to start my preparation and some sites for practise tests?

Thanks for A2A At this moment focus on building a good profile. Try to participate in all events and learn as much as possible. Purchase word power made easy and  do one session daily. You will have  good vocab after 1 month. Try to read as many novels as possible (no to chetan bhagat and durjoy dutta ). Read only The Hindu (no to Times of India) especially its editorials. After 6 months, pick quantum cat and finish it in 6-8 months. Thereafter gives only mocks and analyse them.

Thanks for A2A, but I'd prefer answering this after a few days (once my cat results are out). that would give my answer  some credibility.

Hi.. i am using Arun Sharma's Quantitaive Aptitude. It's a good book.

If you are second year, then this is the right time to built your fundamentals. Most of the students find difficulty with the english section in the CAT, so it is important to better your verbal skills during the second year. As English section has significant weightage to RC it would be important to improve your reading speed and the online reading capability. It is also important that you try reading a lot of varied articles from different sources to make yourself very familiar with all kind of reading. I would also suggest you to use Norman Lewis : Word Power Made Easy to built your vocabulary skills.In the meanwhile you can also start working on quants and try out level one and level two problems after having completed the fundamentals. It is also important to work on LR and start with a puzzle a day to make your reasoining skills better.Work on the above for one year, so that you can start with online testing from third year onwards and you will have 1 full year to test yourself. First six months of your third year spent on topic tests and sectional tests. Last six months on full length mocks.