Sure...
IMO, Tropic Isle in Framingham is the biggest and has the best selection of livestock. If you want a fish, they probably have it.
Uncle Ned's Fish Factory in Millis is decent too. The selection's not as good as they seem to specialize more in FW and koi ponds. But the staff is helpful and they have some nice corals there. That's also where I buy my RO water.
For equipment, like tanks; or food, Pet Club has a lot of stuff as does ***** and Petsmart. (Specialty things like skimmers or LR I usually order online.) I've bought fish from both of these places with mixed success. The employees aren't generally very knowledgeable on SW. Pet Club has LR but it's not very good quality with little to no coralline as far as I've seen.
I'm sure there are other places but I usually end up at either Uncle Ned's or Tropic Isle.
Hope that helps!
Katie