Just when you think the negroni couldn't pack more flavor - here comes the rum! Depending on the rum used - you may need to change the proportions to a little less of campari and vermouth, and a little more rum.
Here is a beautiful (unnamed?) dark bitter variation that was served at Cienfeugos (NYC).
Orange Twist over the rocks
A variation from Michael McIlroy (NYC) - the Right Hand Cocktail uses Antiqua Formula vermouth and adds chocolate bitters.
This cocktail is a variation on the Negroni.