The Digital Book Index

David Dillard writes The Digital Book Index is an ongoing building and already very extensive
catalog of fulltext monographs that have been put online by one or another
website collection of complete works of literature found online scatterd
over the internet.

The Digital Book Index is at digitalbookindex.com

The site says a quiet revolution has been going on in the development of a large library of “digital” or “electronic” books. While there are still large gaps, a very substantial body of “Western” thought is available in the form of downloadable or on-line books. Digital Book Index provides access to more than 72,000 titles records. It is the sole index that gathers both commercial and non-commercial eBooks from more than 1800 publishers and private publishing organizations.