OCLC has made their WorldCat catalog free and available on the web. Worldcat is a catalog of the materials of libraries throughout the country and in some cases throughout the world.
Want to know if a library near you has a book? At WorldCat just enter the title, subject or person. You can do a much more detailed search by going to the Advanced Search.
Does your library not have the book you want? Ask them about their Interlibrary Loan where they can borrow a book from a library for your use.