Matt recenty blogged about the best way to integrate Ajax into a Java webapp and promoted DWR: "The best thing that I've seen is to use DWR, Prototype and Scriptaculous". As the main developer of DWR clearly I'm going to agree that it's a great solution.
Every now and again someone asks about adding a JSP layer on top on DWR, so here's my take.
The biggest reason that DWR has not addressed the issue is that I believe in doing one thing and doing it well. DWR does the RPC thing and it lets you put your data on a page, but we try really hard not to get sidetracked.
I've been tempted to add JSP layer to DWR and I've been tempted to add a widget library to DWR, but resisted both.