UI for acts_as_tree

The current project I’m on requires us to give administrators the ability to modify a tree of models built using acts_as_tree (now a plugin as of Rails 2.0). The acts_as_tree plugin is simple and elegant, but I’ve struggled to find a pre-built UI framework for acts_as_tree that is equally compelling. Can anyone recommend a good, simple (AJAX optional) plugin for generating a UI for acts_as_tree? Please post a comment.