Are you right in Boston? Knowing the neighborhood might help people offer better specifics. Also, not sure how far you're willing to travel to get to a shop.

For what it's worth, I bought a bike from Back Bay Bicycles a couple of years ago. It's located right on Comm Ave. It's a solid shop, but can be hit or miss in terms of service (one of their mechanics is great). If you go there, try to seek out Mike. He races (road/cross/MTB) and is a good fitter. I no longer go there since I moved out of the city.

My bike shop of choice is now the Landry's out in Natick. Probably too far for you, but they do have a location in Boston. My experience in Natick has been great, and their fitting program is really, really good. They do a lot of video/computer analysis and it's not overly expensive.

Hope that's at least a start for you...