I have been a regular user of flipkart.com for several years now. What I like about flipkart is their vast selection of English-language books, both technical and non-technical, both Indian and imported. Their web site is fast and reliable, ordering is easy, and the delivery is always on time (I live in Bangalore). They have discounts on almost all books, and do free shipping.
Flipkart is truly India’s answer to amazon.com. One cannot browse books at an online site like in a real book store, but it is advantageous to browse at a book store, and then order at flipkart for the discount!
My only gripe about them is that they do not stock any regional language books. In the Indian setting it would be very useful if they could do this.