Every one has heard about Google Book and many use it frequently.
The Gov. of India in collaboration with many Institutions is building up a digital library in India http://www.new.dli.ernet.in/ primarily to preserver old manuscripts and make available a number of books (whose copyrights have expired) to the general public.
Only complain i have about the site is that the books are mostly in TIFF format and is not very easy to read. Google Book interface is in contrast searchable and more accessible. For example a search on Astadhyayi on Google books returns many interesting results, but the DLI doesn't return any, though there are atleast two books on DLI on Astadhyayi.