Wine shop near South Station/Faneuil Hall
Second Brix. I also like Federal Wine (closer to Faneuil Hall) a lot.
Brix is newer and shinier. Federal doesn't look like much, but head downstairs into their wine dungeon and they have a really good selection.
Both are pretty heavy on French and Italian bottles, both have incredibly knowledgeable staff. The folks at Federal are perhaps a little longer-winded and more pretentious, but they really, really know their stuff.