15 Play with Google Books Search & Google Scholar

Found Google Book excellent!

It provides a good source linking to bookshops where you can purpose a copy of the item, what libraries may have the item in their collection, reviews that have been posted about the item as well as a link for you to add your own reviews and provide any recommendations about the item.

Google Scholar

Good source where patrons may be able to see an electronic copy of an item / article if it's not available as a hard copy somewhere. The PDF options are fantastic as well.