Okay, I admit it, this is the second post I have made with this recommendation, and I'm a bit of an evangelist.
DWR is interesting and complements YUI nicely with JSON boxing of server side objects. And the YUI, like the others is further complemented by ext.js.
You can look up all of these in your favorite search engine.
Timothy Stone, MIT, SCJP
"This Satan's drink [coffee] is so delicious, we shall cheat Satan and baptize it." --Pope Clement the VIII (1592-1605)