Many books are indeed available for free download (including non-CS books), but most of the ones linked in this thread aren't.

Examples of working links: http://link.springer.com/book/10.1007/978-1-4302-5927-5 http://link.springer.com/book/10.1007/978-1-4302-6131-5 http://link.springer.com/book/10.1007/978-1-4842-0100-8