You never know when some quick reference or thorough research will make you search for specific information. Internet makes things a lot easier sometimes, especially if you know what you need and know the steps of how to get it.

Well, here is one site where information is available for free in the form of E-books:

http://www.questia.com/

Of course we can't miss the Google Book Search

and maybe this one http://www.ebooks.com/

We should not underestimate archive.org's text section - there are millions of items from many different libraries.

Chek here: http://www.archive.org/details/texts

Connexions is:

a place to view and share educational material made of small knowledge chunks called modules that can be organized as courses, books, reports, etc. Anyone may view or contribute:

authors create and collaborate
instructors rapidly build and share custom collections
learners find and explore content

http://cnx.org/

This site is a very powerful resource for many topics and the best is that materials are on academic level and versatile topics and many languages.