No code generation; goal is to provide a Django-like dynamic admin interface with minimal effort. Takes a "either it works for you or it doesn't" approach, because there's no code to edit or customize if you don't like what AutoAdmin gives you. http://code.trebex.net/auto-admin/
Code generation backed by dynamically generated interfaces. Goal is "to bring the declarative goodness of ActiveRecord to the view layer. It manages the presentation, creation and editing of instances of your models, with full-featured scaffolds that include relationship management."
Unfortunately, the streamlined site hasn't been updated in a while. http://streamlined.relevancellc.com/
The newest project, and probably the most ambitious one. Hobo has its own templating language, a library of custom tags, theme support, and user login/access control baked in. http://hobocentral.net/blog/
"A Ruby on Rails plugin that creates an AJAX'ified scaffold for controllers. Sister project of the Ajax Scaffold Generator. Extends the work of the base RoR scaffolds with AJAX and full CSS styling." http://www.ajaxscaffold.com