The Frank Stella's are the best. They are all over the city and they always look amazing. Two of my favorites are the Saatchi and Saatchi lobby (pictured) and the Citi Corp building in Midtown.
Designed by Frederick Law Olmstead (of Central Park), Prospect Park is where I go running in better weather and find an endless supply of flotsam and jetsam for casting in projects all year round. Thickets of trees, hidden paths, and rolling hills are an endless source of inspiration.