I live in Concord and use Keane Fire And Safety Equipment Co.
1500 Main St.
Waltham, MA 02451 781-899-6565
reasonable prices, I drop off in morning, my wife picks up at lunch.
Not much info on the interwebs but Golddiggie sent out this link:
http://www.bfd.org/CO2_fill.htm
I normally do NFG Homebrew just because they're good people.
I go to Igo's and have my 5lb CO2 tank filled. They don't swap it out.
Hey Guys, thanks for the info! I'm actually north of Boston in the Woburn/Burlington area...so i think i might check out Airgas in Billerica, thanks!
I also found this little gem, courtesy of The Worts: http://wiki.wort.org/cgi-bin/moin.cgi/Boston_CO2_Locations
I ended up going to ARCO welding supply in Malden. For 18 bucks I got a filled 5lb tank and an attitude. Might be hard to go back, but they do have the product and no waiting (almost)
I called Strange Brew in Marlborough yesterday and thought I would report what I found for the betterment of beermanity. Their exchange program requires a "buy in" with the purchase of a full 5lb tank for $130, and then the cost for a swap is always $5 cheaper than the general rate. The current 5 lb exchange rates are $20 if you're in the program and $25 otherwise.
A new, full 5 lb tank is $100 without buying into the exchange program.
I also checked with Homebrew Emporium in Cambridge last week and they were charging $100 for a 5 lb tank, and ~$26 for an exchange. I think it was $26.95, but I can't remember exactly.
If you're in Waltham just go to Keane Fire. Super nice guys and convenient hours, they open at 6 or 7AM or something. They don't fill while you wait, but their prices are reasonable for this area. My 10 lb tank is about $20-25 to fill.
I live in Waltham, this place is great. Friendly service and good hours if you work a 9 to 5 (open at 6:30 or 7 I think).