Wow, you might be jumping the gun a bit Tyson.
The problem with planting seeds that are not meant to be planted in winter is that with a warm spell, the seedlings may come up but, with the return of the cold, the seedlings will probably die.
The brassicas should be fine but, Corn (if it is Corn and not a corn salad mix that you have planted) will most likely rot as corn likes really warm soil to germinate.
I know that it is tempting to dive into the garden and start planting everywhere (I've done it myself) but, the best thing that you can do for your plants now, work some good mulch into your soil, keep your compost going and start your lettuces, and what not indoors.
For cover crops:
not frost hardy
Very quick and easy to turn in. Smothers weeds. Flowers attract beneficial insects
hardy to zone 6 (-12C 10F)
Fixes Nitrogen. Annual so won't become weedy Good for winter cover, plant late summer (8-10 weeks before first frost)
Hardy to zone 8, try in zone 7
Fixes Nitrogen. Plant in October on the Coast. Plant in early spring elsewhere.
Hardy to zone 3
Lots of organic matter, can be planted to 4 weeks before frost. Excellant Nitrogen Scavenger
Hardy to zone 4
Fixes Nitrogen. Slow growing in Fall, therefore plant with Rye and Oats. A lot of growth in spring. Quick to grow, great for bees. Sow early spring to summer.
That should be enough to keep you going for a while.