The Norton Simon Museum has a popular Sculpture Garden and Café at the back of the museum. A collection of large sculptures, mostly by French artist, Aristide Maillol, surround a small pond. The café is run by the Patina Group, which also has restaurants at the Music Center and Disney Concert Hall in downtown LA, so at least you can get a decent chicken sandwich. There is also a small lesser-known Asian Sculpture Garden accessed from the Lower Level.
However, I find the most notable outdoor art to be the Rodin collection in front of the museum entrance. Not only does the Norton Simon have one of the 12 copies of Auguste Rodin's six-figure Burghers of Calais, but they also have several of Rodin's studies of the individual figures that he created before compiling the six men into one sculpture. The Burghers of Calais was commissioned by the city of Calais to honor the sacrifice of six wealthy citizens who hostaged themselves to the King of England in 1347 to free their town. In the final sculpture, the six men are in ragged clothes with nooses around their necks. Before creating the composite piece, Rodin sculpted each man alone, first unclothed and then clothed. You can see Rodin's development of these individual characters in those studies on display around the front garden.