I know, everybody knows everything about Google. But just in case you haven't seen this service (still in beta)....
"Finding books is as easy as finding websites with Google Web Search."
Use keywords, phrases, quotations; you get all the books whose contents match your search terms. You might also see a few snippets - sentences of your search term in context.
Click on a book title and you'll see basic info like in a card catalog.
If a publisher or author has given permission, you'll see a full page and be able to browse within the book to see more pages.
If the book is out of copyright, you'll see a full page and you can page forward or back to see the full book.
Clicking on "Search within this book," allows you to perform more searches within the book you've selected.
You can click on any of the "Buy this Book" links to go straight to an online bookstore where you can buy the book. In many cases, you can also click "Find this book in a library" to find a local library where you can borrow it.