Apache Wicket is my current choice when it comes to Java and web apps. It makes integrating AJAX functions a piece of cake: for the most part, you just need to

Apache Wicket is my current choice when it comes to Java and web apps. It makes integrating AJAX functions a piece of cake: for the most part, you just need to call some methods in your Java code. I run apps on Google App Engine with it and am pretty pleased with the performance. Room for improvement: SEO-wise there is room for making URLs look a bit less ugly.