Check out this site: 
http://emacs.wordpress.com/2007/01/16/quick-and-dirty-code-folding/

The main text deals w/ a quick and dirty way that uses a couple of 
commands to hide all the function bodies (class ones too i would 
assume), leaving you w/ just the signature line and the end line.  Also, 
there are some links in the first paragraph to some emacswiki pages. 
I'm not sure which particular folding mode you like from vim, but the 
folding-mode link takes you to a minor mode page that describes how to 
setup emacs to use something very much akin to vim's marker folding 
mode.

Anyways, check 'em out, it looks like there are a number of options.
-- 
Posted via http://www.ruby-forum.com/.