If I have to choose a winner amongst all the Online Book-Stores, it would be Infibeam, with Landmark a close second although it has its own technical issues. e.g. at the time of publishing, landmarkonthenet.com was down! Flipkart.com comes out to be a little costlier. Rediff has its UI issues as I mentioned above. Lastly, Odyssey needs to stock up more books!
Read the full blog post by Prem at http://indianmernoks.blogspot.com/2010/06/review-online-bookstores-in-india.html.