addall.com
The book search engine that allows you to comparison shop more than 40 online bookstores including Amazon, Barnes and Noble, and Borders.
LINK: http://www.addall.com/
books.google.com
Google Book Search the power of Google to find books. It is a tool from Google that searches the full text of books.
freebooksearch.net
Free Book Search is a comprehensive book searching portal with more than 30 search engines in its archive. The site searches hundreds of digital libraries and also scours the net for hidden books.