LibraryLookup

"Jon Udell, Lead Analyst at InfoWorld's test center, didn't set out to rock the world of library technology. He just wanted to check his local library's catalog while simultaneously browsing through Amazon.com. He soon developed LibraryLookup, a bookmarklet that can be installed on a browser's tool bar.

LibraryLookup is a bookmarklet written in JavaScript code that extracts the ISBN from the URL on a bookseller's page, then goes to a library catalogue and searches by ISBN. If the library owns the book, the record pops up. It works with any site that uses an ISBN in its URL, including booksellers such as Barnes & Noble and Powell's, and any library vendor that allows searching by ISBN. Not all integrated library systems (ILS) use the ISBN, but many do. Udell's weblog includes lists of hundreds of bookmarklets already created for libraries that use Innovative Interfaces, Endeavor's Voyager, epixtech's iPac, DRA, and Talis. Users just need to drag the bookmarklet to their toolbar."

Here is the bookmarklet for public libraries in Rhode Island:
RI LibraryLookup
Jon Udell: LibraryLookup homepage