Internet Archive is a non-profit library of millions of free books, movies, software, music, websites, and more. As reviewed by Prof. Scott T. Meissner, Adjunct Professor at the Institute of Biology at UPD:
This is a free online library. All the items on this site are freely available for download, either permanently or for borrowing for a short period. At no charge.
As a biologist I have found this to be a very useful site. Textbooks which are post-copy right are often available there. Classic books, videos, etc, are posted here. If, for instance, a student needed a text book in an area of biology, I would suggest that they search in this site, as often there are books from a few years ago posted here which can give useful background. Some research articles are also posted here.