John Udell has implemented LibraryLookup, an awesome Javascript bookmarklet to look up a book that you're browsing on a site like Amazon, in your local library's web catalog. This is IMHO one of those neat little ideas that are easy to implement, but pure genius to come up with. I found this while researching Joel Spolsky's book "Joel on software : and on diverse and occasionally related matters that will prove of interest to software developers, designers, and managers, and to those who, whether by good fortune or ill luck, work with them in some capacity" (if the title got any longer, we'd have buffer overruns in bookstore catalogs). I'm looking forward to reading this after having devoured his eminently readable online mini-book on User Interface design (Quotable quote on the Windows Help setup "wizard" from in there:

The first problem with this dialog is that it's distracting. You are trying to find help in the help file. You do not, at that particular moment, give a hoot whether the database is small, big, customized, or chocolate-covered. In the meanwhile, this wicked, wicked dialog is giving you little pedantic lectures that it must create a list (or database).

Highly recommended read for long bus or train rides.