There was a recent post on technomancy.us about rinari.el is an interesting mode for interacting with Ruby on Rails projects with Emacs.
I've been playing around with
rhtml-mode.el, and it's making working with the .rhtml files from Rails a bit nicer. Still, the indenting of .rhtml files isn't optimal, it just indents the HTML, not the embedded Ruby code. Still, it's better than standard html-mode for working with .rhtml code, and I think it's worth checking out.
It looks like the rinari rhtml-mode.el is an enhanced version of the old rhtml-mode.