Google Labs have created what appears to be a clever little set o’ widgets.
Its now possible to write an AJAX enabled website using Java as its base language, which then gets translated into HTML, and Javascript. Creating a neat way of developing ajax sites without the headaches of browser quirks and odd effects.
The Kitchen Sink demonstrates all the widgets avaliable to the user, and its darn impressive, the source code is avaliable here.
I cant play with this at the moment due to exams, but its compatabilty with Eclipse is handy for me personally, but its not IDE focused. While it may not provide all the functionality you want from an AJAX site