Bookshelf Gadget - keeps an updated list of library titles checked out, creates a desktop alert when items that I have reserved come due and/or flashes a reminder to renew or return items soon to be due, etc.
Research Gadget - allows direct querying and searching of my favorite library subscription databases without having to log in. Keeps track of login requirements & passwords and better yet it notifies or automatically pulls in articles that meet a specific interest area that I specified.
Programs Gadget - alerts me to programs that may be or interest. Allows me to customize my reminder schedule, so I can register for popular programs as soon as the registration dates opens.
I'm sure there's lots of other possibilities that could be explored. It will be interesting to see how the use of gadget's proliferate over the next year. In the meantime, I believe libraries (and library vendors) should begin exploring and experimenting with these tools to make sure we're there with desktop solutions that will meet new user expectations and needs.
To see a listing of third party gadgets that have been developed, visit the Microsoft Gadget Gallery.