Hey people, here is my first post and I expect you enjoy it.
Have you ever heard about the javascript library Ext JS? If your answer is no, you should visit their website. It's an amazing javascript library, build in the top of Yahoo UI library (another amazing), with a impressive variety of pretty beautiful and fully featured components. It's also extensible, customizable and very well documented. This last point I want to give a special focus, cause the documentation of the api is very good (part are inherit of YUI).
So if you want to deliver web 2.0 applications, don't forget to take a look closely on this library.