OK, this is expensive if you want to buy something! Most people can't afford an Edward S. Curtis for about 12.000 dollars. But where else can you see original prints from Ansel Adams, Curtis, Diane Arbus, and Helmut Newton?
They also have a great photo book section. Not cheap but you can find the books you wanted all your life here!
Also the staff are super friendly and are always willing to show you the top of their collection!
The best photo gallery I've been to! And no entrance fee...