Live Search Books
Microsoft has a new beta service — Live Search Books. They have been scanning books in some of the major libraries, e.g., the British Library, the University of California, and the University of Toronto, currently provide access to these works. They will soon also include books from the New York Public Library, Cornell University, and the American Museum of Veterinary Medicine.
It uses the same search engine as Windows Live Search and provides keyword searching of these texts. At this point, Live Search Books only provides non-copyrighted books. Ultimately, they will provide access to copyrighted books for which the publisher has given permission.
The results page allows you to download the entire book in PDF, search inside the book, and provides links to specific pages which have your search terms. You can also page through the book itself.