Okay, so somebody mentioned Oona's, which is awesome, IMO. That is right off of Harvard Sq. too, so definitely stop there when you visit the discount-basement Urban Outfitters.
Boomerangs is a thrift store, there's one in Jamaica Plain on Centre St., but it's a chain and there are more locations. They have some cool stuff most of the time.
Will you have a car at all during your stay? Any Salvation Army or St. Vincent's is good. Look them up in the phone book, or http://www.switchboard.com
They have several near downtown that you may not even need a car to get to.
Looks in Cambridge is awesome. Although I haven't bought anything there yet so I can't vouch for their prices. They are off of Rt. 2A. You can walk there from Harvard Sq., it'd take about 10-15 minutes.
While you're in Harvard Sq also check out the brand new Magpie on Huron
. These guys posted in the Craftster classifieds recently, and I plan on consigning with them.
There is a great little place in Brookline (corner of Rt. 9 and Cypress St., 131 Cypress) called Cafe Society. Get there in the middle of the day, because they have weird hours. As long as you're there between noon and 6pm you should be golden, including Sat and Sun. You can take the green line there - it's right by the Brookline Village stop.
Oh yeah there's also Fabulous, Inc.
in Inman Sq. (not too far from Harvard Sq., take the bus) But I think she's kind of overpriced, esp. for the clothes. Still, Inman Sq. is a cool area, and it'd be worth the trip to check out the Zeitgeist Gallery
The South End Open Market was all craftsters, every SUnday, but they stopped doing outdoor booths at the end of November. They are having a holiday (indoor) show though, in the same location - South End Holiday Market
. I definitely have to go to that.
Other events happening in the next 2 weeks are Bazaar Bizarre Boston
(Dec 11th) and Crafts at the Castle
(Dec 2nd - 5th).
Again, if you can get a car, Providence RI has Craftland
(ongoing until Dec. 21st)
Hell, now I think *I* need to print out this list so I don't miss anything!