GWT 1.5 Milestone 1 is available now. Check here for more. Now it supports Java 1.5 syntax fully. Wow right? Congrats and Thank you GWT team for the great job.
GWT4NB is the GWT plugin for Netbeans. Check the article here to get started.It looks neat and really help full for the starters. If you are Eclipse user, like me, you can check, Cypal Studio and GWT Designer. GWT Designer is commercial and it got graphical editor, have features like previews, drag and drop (Both features are very useful for prototyping, can not rely on it for production) . Try the trail version before going to buy the license. For me, Cypal Studio, is more than enough to get the job done.