I'm not kidding, and this is no exaggeration.
history of Google Books makes good reading itself.) Now you can search the full text of tens of millions of volumes. Access to view the contents depends on the level of access publishers and authors have granted Google users in the wake of a groundbreaking agreement in 2008, but many books are available in full view or preview (which is fantastic for research). Others are available in snipit view, or simply as citations with links to locate the physical book in a bookstore or library (or to purchase the eBook on Google Play if available).
HINT: There are ways to access only full-text books on Google Books, and there is an easy to use "Full View" option in the left-hand column after performing an initial search. Public domain books (and some other full view books) can even be downloaded as a PDF in their entirety or as "clips" (images taken from the book). See The Tragedie of Hamlet for an example of these functions.
My favorite feature of Google Books is the ability to search the content of a book for any word or phrase. Google Books finds every instance of the search term throughout the book (using optical character recognition, or OCR), provides simple links to each page, and highlights the term in the text on each page. Visual markers on the right side of the screen identify other places in the book where the same terms appear. Imagine the applications for a student searching for direct quotes to back up their thesis... or for your own research - as part of your graduate work, a grant writing effort, or any research-based decision making.
Another of my favorite features is the embed feature, available for any full view (or preview) book. This allows you to embed the book right into another site (such as a Google Site). The embedded version of the book is also searchable and can be used to find every instance of a search term within the text. So, a teacher can setup a site dedicated to the study of a particular book (or topic) and embed the book (or books) directly into the site for easy student access.
The video below illustrates the search and embed features of Google Books for a hypothetical final project for a unit focused on Crime and Punishment by Dostoyevsky.
Google Books has a number of other powerful features, particularly if you're logged into your Google Account, in which case you can save books to custom "shelves" in your own online library (called "My Library"). Shelves can then be shared with students and colleagues as a way to disseminate curated resources... and shelves can then be searched.
You might also appreciate the 3D viewing option. (But, um, you need 3D glasses.)
To learn more about Google Books, start here or join us for a Google Apps in Education Summit in your region. I'll be leading a search workshop at each event. :)