There is an Emacs mode for working with Ruby on Rails (of course). The main project page can be found here. In order to get everything set up, I had to do the following:

1. First download the latest release of the project and extract it into your emacs library directory. I install most of my extensions into a directory of my $HOME called "~/my/cfg/emacs". This creates a subdirectory called "emacs-rails".
2. I then added the following lines to the end of my .emacs file:

   (setq load-path (cons 
                               (expand-file-name "~/my/cfg/emacs/emacs-rails") 
                               load-path))
   (require 'rails)
   

3. The package depends on the emacs lisp files in the ruby distribution's "misc" directory. If you don't have them, grab a copy of the ruby tarball, extract, and install them in your emacs library directory.
4. The package also depends on a emacs function called "find-recursive", which I grabbed from here.

EDIT - OK, more useful to me at this stage is rhtml-mode which gives me syntax hi-lighting for rhtml files and can be downloaded here. Also apparently rinari is the successor to emacs-rails.