As discussed, the more you move towards a stateless controller and JavaScript Remoting client architecture, the more you need to invest in providing or obtaining client-side components not presently provided by Salesforce.
Consider this decision carefully on a per-case basis (not all of your application UI has to use the same approach) and make sure that you appreciate the value of the platform features that you are leaving behind. Expect to adjust your expectations around your client developer's velocity to be more in alignment with those on other platform developers.
Libraries such as JQuery provide a great deal of convenience, flexibility, and components available in the community to provide some alternatives and improvements over the Visualforce components, in addition to larger components such as grids and trees. Taking things a step further, larger commercially available libraries such as Sencha ExtJS are also usable from within a Visualforce...
