If you're not feeling particularly creative but want to try something a little different, take a basic cocktail and swap out the base spirit. For example, take a Manhattan, replace the whiskey with Scotch (I like a blended Scotch like Famous Grouse, or Black Grouse for a touch of peat), and you've got yourself a Rob Roy. Make an Old Fashioned, but use an aged rum (I like Zacapa, but have several others on hand that will work as well) as your base spirit and you've got a lovely Rum Old Fashioned like the one pictured above.
Rum Old Fashioned
1.5 ounces Zacapa 23 rum
1 scant barspoon simple syrup
2-3 dashes of bitters (I use either Angostura, Regan's Orange, or Bitter Truth Aromatic Bitters, or some combination thereof)
Stir ingredients in a mixing glass with ice until well chilled, then strain into a rocks glass, preferrably with one large ice cube (try this