My personal favorite (because I made it
) is:
http://wiki.battlemaster.org/wiki/Template:Message2Instructions are right on that page, included copy/paste-able code. It also uses color coding to simulate the in-game colors for the various message types.
This template posts everything in
(boring) shades of gray:
http://wiki.battlemaster.org/wiki/Template:MessageSomeone did one similar to Message2 that colors the entire message box, not just the header. I don't remember what it was called, and a quick search didn't find it.