http://www.freepint.com/issues/140705.htm#tips
"Free Public Domain and Copyrighted e-Books Online"
By Sam Vaknin

"By far the largest and best maintained index is John Ockerbloom's
Online Books page, with well over 20,000 individual items listed
< http://onlinebooks.library.upenn.edu/ >. It offers links to new books
almost daily < http://onlinebooks.library.upenn.edu/new.html >. Browsing
through this index is bound to get you virtually everywhere. There is
rarely a (legal) book online that is not listed here"

This is not true.

1. OBP has 20,000+ free books
http://www.digitalbookindex.org/ 60,000+

It is recommended to use both listings. Example: keyword metaphor brings 6 books (OBP 4, DBI 5).

2. There are some large collections (and a lot of small collections) NOT in the OBP (nor in the DBI).

Examples of large collections with English books not in the OBP

http://www.archive.org/details/texts

http://link.library.utoronto.ca/booksonline/
800+ titles

OHIOLINK Brittle Books
See http://archiv.twoday.net/stories/442689/
400+ titles

UMich Digital General Collection
http://www.hti.umich.edu/cgi/t/text/text-idx?c=genpub;cc=genpub

Gallica
http://gallica.bnf.fr/
Hundreds of items.