Headed by Italian bartender Franscesco Cavaggioni, Belmondo is the third great opening of 2010 in Madrid (with Cabrera and Dry Martini Madrid). The place is small-ish with great design -- look out for the cointreau bottle-filled ceiling -- and they have a big outside area in the summer -- in a quiet and shady spot.
Their menu mixes classics and contemporary drinks made with good ingredients and craft methods. Notable cocktails include the Basil Julep, Smokie Romero (Tequila, Agave Honey, Rosemary, Lemon Bitters), the Gringo (Tequila, Conitreau, Balsamic Vinegar, Lime and Fig), a variation Boudreau's Rubicon and the Zacapa Manhattan (Zacapa 23, Pedro Ximenez, Orange Bitters, Cherry bitters).
Although it's outside the "normal" cocktail route, you cannot make the economy of the visit.