Ebooks: Free Ebook Collections

The DPLA offers a single point of access to millions of items photographs, manuscripts, books, sounds, moving images, and more from libraries, archives, and museums around the United States. Users can browse and search the DPLA's collections by timeline, map, format, and topic.

Nifty, although it doesn't always provide the full text.

HathiTrust Digital Library is a digital preservation repository. It provides long-term preservation and access services for public domain and in copyright content from a variety of sources.

Mostly older content from books no longer in copyright. Check out the bookshelves by subject to browse.