Speedbar is an Emacs Lisp program which allows you to create a special
skinny frame with a specialized directory listing in it. This listing
will have both directories and filtered files in it. You can then load
files into your emacs frame, or expand the files to display all the
tags that are in them and jump to those tags. You can also expand
multiple directories into your speedbar frame.

WWW: http://cedet.sourceforge.net/speedbar.shtml