Your zone is tricky, I'd love to hear if you have success growing anything over winter. I know parsnips are supposed to be good - they keep alive under snow and in frozen soil, but won't really grow until it warms up a bit. I've heard about the Brussels sprouts from a few northerners (zone 4 anyway, not sure about 3). You essentially grow them in fall, but the world acts like a natural freezer, keeping them fresh until you're ready to use them.
Do you have any cold frames or similar structures to give winter plants a bit of protection?
I actually don't have anything growing this winter either. I moved in November, which meant I just couldn't get things started in summer/fall to plant out, and I'm in a whole new zone here, much colder than before. Next winter will be an adventure for me!