Ed Ruscha, 'I Think I'll...', 1983: Associated with Pop Art, Ruscha has worked in painting, printmaking, drawing, photography and film. His works now fetch significant prices.
Josef Albers, 'Homage to the Square: Midday', 1954-57. Albers, a German-born American artist, was a student at the cutting edge Weimar Bauhaus in 1920. Two of his 'Homage to the Square' series have been lent to the Obamas.