'Course my favorite of late is by United Healthcare. It's out on the Serengetti, where a Researcher has an Assistant with a lion mask slowly walking toward a pride of Lions, urging him on. The lion is watching him, and the researcher reminds the masked Assistant to stand his ground, then says "Begin Agitation Phase." Assistant growls, and it cuts with the Lion headed toward the Assistant. I laugh like hell every time.
That, OTOH, is a very funny commercial.