One of the most interesting pieces of art is the building itself. Beside its modern architecture it's very nice illuminated at night (the red one).
Right in front of the SFMOMA there is a interesting park, maybe it's modern art, too. It's name is Yerba Buena Gardens. From there the look at the MOMA is even more impressive.
There are not so many plants in Yerba Buena Gardens, but they look very nice. There are also some fountains (in the background).