Have you ever shopped for books online and wondered whether the library owns copies (before you plunk down your credit card)? John Udell has created a "library bookmarklet" that creates a button for your browser's Links toolbar. The bookmarklet button gives you one-click access to your library's catalog from any screen that includes an isbn, including pages from bookstores like Amazon.com, Bookfinder.com, etc. If the library has the book, you should see the catalog listing and be able to request it with your library card number.
Here is the Bookmarklet for Sacramento Public Library:
Find at SPL
Drag the link to your links toolbar, or right-click, select "add to favorites", click "yes" at the security warning, and save in "links". (If you have a long list of links, you can drag the bookmarklet to the top of the list or to the place you want it to stay on your links toolbar.)
Problems dragging your bookmarklet to the link toolbar? See this screencast.