IntelliJ IDEA 9 allows you to complete tags for components with namespaces imported in the current GWT ui.xml file.
In IntelliJ IDEA 10 you can complete component even if it is not imported yet. Just press Ctrl+Space twice and IntelliJ IDEA will search for components across the whole project and libraries:
After pressing Enter the IDE will complete the selected component and insert the appropriate namespace declaration for it:
Try IntelliJ IDEA EAP and code faster!