Hey there, I live in Boston as well. What kind of riding do you want to do? Boston offers a lot of different terrain which can lend itself to different types of bikes. I know they can be pretty expensive, but I recommend you start your search by narrowing down the type of riding you want to be doing. Once you figure out what kind of riding you want, I would say look on boston craigslist. This is definitely a biking town and there are tons of people in the area selling bikes that won't cost you an arm and a leg. It would definitely get you a great bike at a good price, and it would be easy and relatively cheap to replace some of the more worn components if you needed to.
If you really want a new bike, I would recommend Landry's on Comm Ave or Back Bay Bicycles on Mass Ave. Both of these shops offer test riding which is really helpful, and both employ super-knowledgeable staff that can help you pick the one that's right for you.
Last edited by tgf; 07-23-08 at 11:00 PM.