Project Gutenberg offers over 38,000 free ebooks: choose among free epub books, free kindle books, download them or read them online. They carry high quality ebooks: All the ebooks were previously published by bona fide publishers. They digitized and diligently proofread them with the help of thousands of volunteers.
Using Project Gutenberg is easy, with both a general search / browse interface and a more advanced search feature.
Basic Search and Browse
The advanced search interface