I’m really impressed with Hobo for Ruby on Rails. It brings a much-needed higher level of abstraction to views, allowing you to use and create your own tag-oriented components — much like Java and ASP tag libraries, but in an elegant, Railsy way.
Plus, there is updating of page regions with Ajax and a completely fleshed-out user permissions system built on acts_as_authenticated. Follow the link for screencasts. You’ll be glad you did.