Triathlon stores in Boston area?

I like Quad Multisport in Arlington heights (1341 Massachusetts Ave.
Arlington, MA 02476  -- telephone  (781) 646-5600 -- web http://quadmultisport.com/).

The website sucks (one page) but the store is large and well-stocked and they do rentals. The store is a spinn off from Quad Cycles, which used to occupy the premesis but is now closer to Artlington center but still on Mass Ave.

Arlington heights is not central, but can be reached by a short bus ride from the end of the Red Line subway at Alewife.

Just realised that you are in Cambridge -- Quad Multisport is just a block from the Minuteman Bikepath near the lights at the crossing in Arlington Heights. You can cut through Golds Gym parking lot from the bikepath, there is a gap in the hedge near the road bridge.

I want to second the recommendation for Quad Multisport, which is actually now called V3 Multisport (the co-owners of Quad cycle split the business).  They have a good selection and they are super nice and supportive.  They sponsor a lot of local events, too.  When I bought my first tri shorts and top, one of the sales clerks very quickly took over for my well-meaning but clueless husband and brought me several options to try on, and gave me good advice on what to look for in terms of fit.  It was a great experience, and typical of the store.  

FastSplits in Newton, ask for Brian he is the manager and a great guy.

Landry's in Comm Ave. Ask for Mark, also the manager and another great guy.

Can't say enough good things about Fast Splits and their manager, Brian.  I travel from the Spfld. area (about an hr) just because of the awesome cust. service!