Newbury is a chain now (I don't know if it always was), so there are ones within driving distance (and convenient parking) -- ones that don't involve navigating the streets of Cambridge (and Somerville and/or Arlington, depending on my route). I like my local indy shop. Ben gets Yu-Gi-Oh and sports cards there, and I bought Fray there. They have an enormous collection of old stuff, too.
Despite the name, the amount of comics they have may vary by location. I'd expect the in Boston/Cambridge stores to have the Buffy comic, but I'm not so sure about further out of the Hub; they've been more of a music store (and lately general pop-culture geegaws) for yoinks now.