The GWT team has just announced that the GWT incubator project is now up and running. It is hoped that the GWT incubator will eventually contain several widgets submitted by contributors, where they can be discussed and reviewed by all. The best of these might eventually make their way into the GWT libraries themselves. Hopefully this will help us reduce the duplication of similar widgets resulting from the numerous GWT widget libraries out there.

Check out the first couple of projects that have been seeded for examples:
ImmutableResourceBundle
StyleInjector