The Stanford Graduate School of Business: Jackson Library: FastJack toolbar is one of the more comprehensive library related toolbars I've found. It's also interesting from an OU point of view because the Jackson library use the same system as the OU Voyager system.
I was going to write a blog giving a tour of the features, but thought a screencast may do the job even better. So here it is (apologies for the poor audio quality): MyJack toolbar screencast.