Yahoo has published a pattern library. A pattern is a optimal solution for a common problem.
A pattern is presented with a title, the problem, the context and the solution. You can also go in and test the solution your self. Nice!
Each pattern also have a blog entry, where users can put their input.
You can also download stencils to a lot of different programs:
Fireworks, Omnigraffle, Axure, InDesign etc.