Can't figure out any reason to plant an annual ground cover to get it working and have some organic matter to till in next year....
Any ground cover will also come with seeds unless you are very careful to till in in before it flowers.
But if you are determined, I would use a red clover or alfalfa....and get it plowed under before it sets any bloom or you will be fighting the stuff for years.
Why notjust lay down fine pine wood chips, and plant the basics this year? There is little value inall that digging and mulching and tilling....it will soon settle, getlots of organic stuff ON the soil and the worms will take it down. Every time you till you expose more weeds to grow.Just mulch well with wood chips ( or chopped leaves or grass clippings, provided there have been no herbicided or weed killers used) and plant.
Lots of stuff will do very well planted in the fall.
Linda C

Red Clover or Crown Vetch would both help to fix nitrogen, which will enrich your soil;
as Linda said, though, be sure to turn it under before it goes to seed!

You might also post on Organic Gardening or Soil Compost & Mulch.

Best luck, & have fun!

Wow -- I feel like a total newbie now.

I thought the point of an annual was that annuals would just die and wouldn't return at all. I didn't realize they seed and spawn new annuals. Doh!

If you're doing a cover crop then part of the sequence is to actually cut the crop before it comes to flower so you get plenty of juicy material that rots down quickly - and has enough fibre to not make a felted mess (like you see with heaps of grass clippings.)

The roots stay in the soil and, as they rot down, add even more humus to the soil.

It is really important to not bury the cover crop deeply, It can combine with clay to make a bit of a toxic brew for a while. If you live in a rural area observe how the farmers disc in the crop residue (hoping that they don't burn off.) You might also notice that some farmers turn stock onto the crop residue to clean up and add manure before they disc. You'll need to have an acceptable process to add extra nitrogen to the soil as the cover crop rots down. Something slow acting, such as blood and bone could be useful, although it can attract animals. Perhaps dried animal manure would be an alternative.

Your biggest hassle would come if you have a perennial weed (like dandelions, dock, twitch grass, or whatever your local nightmare/s happen to be) growing in your cover crop. The darned things LOVE being disced. It spreads little bits of root everywhere - and, being weeds, they usually all grow.

A cover crop can be highly useful in a poor soil - and to give protection if wind or heavy rain moves soil in your area.

You might also want to consider growing a cleaning crop such as potatoes, or rows of peas that need regular weed control and/or hilling up. If you were to lay down a mulch between the rows, along the lines that lindac has suggested, then you could have 'the best of both worlds'.

If you do decide on doing the cover crop - and leaving it over winter (a ryegrass, mustard, lupin, barley, clover, vetch crop would probably all be suitable) remember to leave enough time between the cutting back, digging in - and your planned planting date - for the material to rot down, or plant crops that will tolerate quantities of partially rotted material in the soil.

Also think about any fertiliser/liming that needs to be done, too. Those additions need time to become effective in the soil for following crops - and some crops don't like them too fresh.

In the midwest of the USA, they are practising "no till farming". Thes tubble remains in the field all winter and in the spring the crop is planted without plowidn, discing or harrowing.
Saves top soil form blowing andw ashinga way, adds organic matter to the soil ands aves labor...and gasoline.
Von, if you want to get the benefit of a cover crop, of green manure, toss in some alfalfa pellets...lots it's impossible to add too much...well almost impossible.
Linda C

Here is a link that might be useful: about alfalfa