Google Scholar provides a simple way to broadly search for scholarly literature. From one place, you can search across many disciplines and sources: peer-reviewed papers, theses, books, abstracts and articles, from academic publishers, professional societies, preprint repositories, universities and other scholarly organizations. It is also very useful for seeing if other scholars have cited a book, article, etc. Search on the title, and then follow the "Cited by ..." link.
Index of literature covering the history and culture of the United States and Canada, from prehistory to the present. The database indexes journals from 1964 to present and includes citations and links to book and media reviews.