A small exhibit, Howard Pyle and Illustrators of the Brandywine School, is at the Federal Reserve Board's headquarters, on 20th Street and Constitution Avenue NW. I saw it earlier this week. The art is mostly from the Free Library of Philadelphia and includes some Pyle pirates and other illustration work, some original Maxfield Parrish paintings, and a lovely book cover painting - The Cobra's Head by Frank Schoonover.
There's only 24 pieces in the show and you have to telephone for a reservation at least a day in advance and then go through a metal detector and be accompanied by a guard, but the artwork is good. The number is 202-452-3778 and the show will be up through March 30. Admission is free, and they give you a nice full color booklet.