I recently came across:
This website contains catalog of numerous books in the public libraries in West Bengal. Many books that are obsolete now, or hard to get hands on, are there. But the most interesting part is: this website stores the SCANNED E-Book versions of the books that are freely downloadable. The website is also easily navigable.
I browsed the History section. This section contains more than 450 books on History specially History of Bengal. The other sections are also pretty rich.