Skipton's is good. That's in Boston, near 93, but it's a little difficult to get there. They often have some real weird FW stuff that no one else has, but their selection varies quite a bit week to week. I've picked up some really cool stuff there though, so it's definitely worth a trip.
www.skiptonpetcenter.com is their website, they have pretty good directions. Not much else in Boston proper unfortunately, I think there's a decent store in Quincy, but it may not be there anymore, hopefully someone else can confirm that one. If you really get bored, about 30-45 min north of the city off 93 there's 2 good stores. They're in Salem NH but they're really easy to get to. One is Seaworld, the other is Jay's aquatics. If you want directions, PM me.