Not just for scholarly reference management: Zotero is a great tool to keep track of the books you have if your personal library exceeds one or two Billies in volume. For books printed after 1970 the ISBN alone is enough to have it fetch the most relevant metadata for any book published anywhere from online catalogues. I find Zotero particularly useful when going to a book-fair; it is easy to export a list of titles and authors of books you own so you can easily reference it to see which books from a particular author or series you already have.