Google Books
Google Books makes only selected pages of some ebooks available to you to read on a page-by-page basis (previews). Google Books offers the following text-viewing options: Full View, Limited Preview, Snippet View, or No Preview Available. More details about what you can see in these views.
Internet Archive
Internet Archive contains nearly 4 million "texts" (mostly ebooks). The archive also offers streaming video and audio (including music) files.