Readers like to search Amazon.com or other booksellers' sites to find books of interest and then wonder if the book is available at the local library. xISBN bookmarklet makes this easy: when you have a book information page from an online bookseller displayed in your browser, you simply click on xISBN bookmarklet to automatically check your library's OPAC for books with the same ISBN and other ISBNs related to the book. The version 2 of liblook implementation, which is integrated with Worldcat Registry and supports thousands of libraries.
Here is instructions on how to link to xISBN Library Lookup service.
LibX supports for xISBN. Here is a screen cast that shows how it is using xISBN