Here are some free online book sites with with comments.
There's really no standard for how these things are done, so your requirement to be able to page through the entire thing directly is not always satisfied.
That would be nice!
http://www.promo.net/pg/ Project Gutenberg. Generally texts are taken from books published pre-1923. (It's more complicated than that but 1923 is a good first rule-of-thumb for the U.S.A.)
http://digital.library.upenn.edu/books/ 20,000+ Listings
http://www.classicbookshelf.com/library/ no apparent count. Applet for reading.
http://www.theworld.com/obi/ directory listing; eclectic. not "organized".
http://www.ipl.org/div/books/ ** 20,000+ books. Very nice.
http://etext.lib.virginia.edu/ ** --The Electronic Text Center's holdings include approximately 70,000 on- and off-line humanities texts in thirteen languages, with more than 350,000 related images
http://www.literature.org/ various works online, free. author search
http://un2sg4.unige.ch/athena/html/authors.html various works online, free. author search