The newly-released Direct Web Remoting (DWR) library greatly simplifies AJAX with Java Web applications.
For advanced developers, DWR does a great job of integrating with Web application frameworks, is fully extensible with pluggable data types and object instantiation methods, and even comes with built-in support for the Spring framework.
While DWR is certainly the newest, I’m sure it’s not the only library for remote scripting with Java Web applications. Have you used another? If so, I’d like to hear about your experiences with it.