WorldCat is an amazing resource as it is a portal to a good portion of the world's libraries. Even Seattle Academy's library holdings are included in WorldCat.
Use this catalog when you want to see almost every book ever published on a subject or if you wish to see all editions of a particular book. If you specify a zip code the catalog will list which libraries near this zip code hold a copy of that book. Citations in many formats are also available for each entry. NoodleTools also pulls some of its citations from WorldCat.