Google Scholar (Beta) "enables you to search specifically for scholarly literature, including peer-reviewed papers, theses, books, preprints, abstracts and technical reports from all broad areas of research. Use Google Scholar to find articles from a wide variety of academic publishers, professional societies, preprint repositories and universities, as well as scholarly articles available across the web."
Link via Amardeep Singh, who says "Scholars are increasingly prone to googling subjects before going to library catalogs, World-CAT, or the MLA Bibliography. Google is just faster, simpler, and more up-to-date than slow, CD-ROM based databases that require log-ins and proxy servers. If you can find a book on a topic you're looking for through Google, why go to the library website?
"Of course, that short-cut often creates a problem, which is that you get a lot of personal websites when what you really want to know is: who's published something serious on this? As much as I enjoy doing this blog and am pro-blogging in general, sometimes you want books, not blogs. Scholar.google fixes that problem, and cuts out anything that isn't a journal or a book pub."