Ebooks that cover many disciplines and are usually more recent.
EBSCO eBooks provides ebooks from a variety of publishers. Older academic titles and newer popular press titles (e.g. cookbooks, juvenile texts). Platform is fairly easy to use and books can be read entirely online. Print and download options are clearly listed. Subscription.
As of June 2, 2011, free PDF versions of all books published by NAP (more than 4,000); publisher of National Academies of Science, Institute of Medicine, and others.
Large collection of digitized books that are freely available. Most are older.
Project Gutenberg is a volunteer effort to digitize and archive cultural works, most of them in the public domain. Most are in plain text format, some are available in other formats such as HTML, or Kindle. Free.