German Expressionism makes me giddy. All my favorites are here at any given time - George Grosz, Otto Dix, Egon Schiele, Gustave Klimt - and the building was designed Carrére and Hastings, the same architects that designed the New York Public Library.
The best underground shows you will find will have free pbr and models as far as the eye can see. They are rarely announced, so keep your eyes out for promising openings, especially with Milk Underground coming up.