Zotero is a free, open source extension for the Firefox browser, that enables users to collect, manage, and cite research from all types of sources from the browser.
LibraryThing "[has] Zotero support on all book pages. From that you can create book lists and export to any number of bibliographic formats. It's really the way to go because it offers management of various sets of books, tags, etc. Once you install the FF plugin a little book appears in your address bar to allow you to add that book to your zotero collection."#4, conceptDawg