I saw this one over on the Playfool blog. Apparently, Yahoo has a new Design Pattern Library over on their Developer Network website. JavaScript Source code and examples are available for several common UI design patterns including the following:

Autocomplete
Breadcrumbs
Drag and Drop Modules
Module Tabs
Navigation Tabs
Object Pagination
Search Pagination
Rating an Object
Writing a Review

Some of these are really cool. I especially like the drag and drop module as this is something I've been looking to do in a portal application we have. It will be interesting to see how the library develops as more people start contributing.