I've always been a fan of the LibraryLookup project; it's a simple tool that, given an address containing a ISBN (e.g. an Amazon page), it will search your local library catalogue so that you can see if the book is available.
Unfortunately, the Bookmarklet Generator option for Talis-based systems doesn't work for my local library in Stockport (UK), so I googled a bit and found this post on a Talis blog, which gave me the correct syntax.
So, here's the resulting bookmarklet (drag and drop the link on your bookmark toolbar, check this link if you don't know how to): Stockport Library.
