Contains over 140,000 ebooks that you can read online or download. Titles also appear in the Library Catalog, but going direct through this link will let you search the full-text of all the books and browse every title. (Formerly ebrary.)
This site offers full text, and photos, for out of copyright books, and "snippets" for those not in the public domain. The snippets themselves can be useful, and may lead you to interlibrary loan requests.