Gallery Kayafas, the Photographic Resource Center at Boston Univeristy, Howard Yeserzki Gallery, Clark Gallery out in Lincoln, MA. Yes... the MFA is well worth a visit, though I'm not sure what photography they are showing at the moment, but if you head out to the Clark Gallery, then a visit to the Decordova Museum is a good idea. There's a small gallery specializing in vintage 19th c. photographs in Winchester called the Lee Gallery, and also in Winchester, the Griffin Museum of Photography.
If you are here in Sept. there is the New England Photo Biennial being shown at the Danforth Museum in Framingham. I have two prints in the show, and I think there will be some of David Prifti's wet plates there. The opening reception is on the 12th of Sept.
I'm not as familiar with galleries on the Cape, so I can't really help there, perhaps Drew will chime in with some thoughts.