This week's book giveaway is in the Agile and other Processes forum. We're giving away four copies of The Mikado Method and have Ola Ellnestam and Daniel Brolund on-line! See this thread for details.
It looks like DWR (an Ajax framework) has some kind of a Spring integration. Haven't used it myself, though.
In fact, I've only used the Ajax stuff built into the Ruby on Rails framework and I've used the Prototype JavaScript Framework "manually", that is, writing JavaScript using the Prototype library for making Ajax requests etc. I guess I didn't even feel a real need to have an "Ajax framework" beyond Prototype.