Woohooo - Google Web Toolkit allows you to write cool Ajaxified apps in...Java!

A compiler translates UI code to javascript and HTML. No more fighting with the many javascript and Ajax tricks required to make client-side apps really work. Well, that's in theory at least, we'll have to eat that pudding for a proof.

In development mode, your app runs as server-side Java, which makes debugging your much easier than with handwritten javascript code.

I've only had a quick look at it, and for now the only downside seems to be the binary-only compiler. But all the tech looks really good, I'll have to take a closer look.