Recently I was looking for ways to find programming books and manuals. Below is a list of sites that help to make this easier.
Search Free E-Books
PdfGeni.com - Free PDF e-book Search Engine
PDF Search Engine - Free E-Book Search
Data-Sheet - PDF e-book data-sheet manual search engine
Scribd - Share your documents online
E-Book Collections Online
Gutenberg - the first producer of free electronic books (e-books)
FreeComputerBooks.com - Free Computer, Mathematics, Technical Books and Lecture Notes, etc.
FreeTechBooks.Com - Free Online Computer Science and Programming Books, Textbooks, and Lecture Notes
OnlineComputerBooks.com - Free Computer Books, Free e-books and Books Online