Yahoo Design Pattern Library
Yahoo have their own design pattern library, called Yahoo Stencils, which might be interesting for every user interface designer. Stencils include visual proposals to different recurring user interface problems. This includes calendars, charts, banners, navigation, screen resolutions, tabs etc. They give us ideas how we could design, document and reuse interface elements that are pleasing and completely transparent for the users. Yahoo Stencils are downloadable in a variety of formats.
If you are interested in user interface design, you can also take a look at the book "Designing Web Interfaces" by Bill Scott and Theresa Neil.