Definitely check Filene's Basement; it'll most likely be their Boylston Street location because their Downtown Crossing location won't be open for several more months; in fact there was just an article in the newspaper that that location has a good six more months for the renovation project to even continue due to the funding/economy issues.
Another great shop that you could check is the "Bridal Stock Exchange" in
southern New Hampshire,
http://www.bridalstockexchange.com/
Here's a recent article about their incredible sale they recently had for military brides, it was quite an idea! One woman even flew here from Cincinnati, Ohio:
Dresses for Military Brides | NH Wedding Magazine
One more place for you to check out. This is a gem too, so hold on to it, trust me! I work with this Greek woman that dresses absolutely incredible, JUST stunning, one day we were talking about gowns and she told me that her favorite place to buy gowns AND to have them made here too is this shop in Lowell, MA. called "Chantilly Place". It's located at 107 Merrimack Street in Lowell. (978) 446-0700.
This shop does pageant gowns for the Miss Massachusetts/USA contestants that's how popular and good it is here. I wrote the info down for my nieces for down the road, so here's the scoop on it! It's open on Tuesday - Thursday from 12 -8, Wednesday & Friday 10-4 AND on Saturday 9-3. So that's another "good" one to remember and to check if you're up for cruising out of the Worcester area; some day soon.
I wish you the Best of Luck & also Best Wishes for a happy, fun wedding & wonderful new life together.