Easier Mockups from Rails with Showoff
Showoff is a new Rails plugin that "provides an easy way to include and show off HTML/ERB/Haml mockups." Creator Adam McCrea has put together a blog post explaining how it works.
Essentially, Showoff provides a way for you to bring mockups into the standard view/layout setup, rather than the common route of just dumping HTML mockups into your /public folder.
Showoff requires Rails 2.3 as it's an Engine-style plugin.