The most enthusiastic proponents of winter gardening are Eliot Coleman and Barbara Damrosch and they live in Maine.
http://www.vegetablegardener.c...
Of course, you can't grow tomatoes and peppers, but you can grow a wide variety of cruciferous vegetables and Asian greens.
We have already learned you can make a 4 x 4 piece of ground very productive. Put a cold frame on it, and it should be a great way to have some fresh greens in winter.
I haven't tried this yet, but Ive been buying up old windows to start an experimental cold frame this winter.