I think, if you are in zone 6, probably it is too ate to grow any cover crop that can be tilled in as green manure.
Other than beans, most gardeners plant rye, annual grass, clover, fenugreek. But for spring growing it is another thing.

Another point is that you would want to grow things that their roots are nitrogen fixer or their foliage is rich in nitrogen. I don't think, for example, radish is one of those.

I use a lot of cover crops, and in late summer and fall I love mustard greens best. You can take a couple of cuttings for the freezer, then chop in whatever is left before the first hard freeze.

It's late to plant seeds, but I have a couple of flats of crimson clover plugs, started from seed in early Sept, that I'll use as bed-sitters through the winter. They will have to be covered with wire cages or the deer will eat them.

I have some oats holding seed now, and I'll let that stand and winterkill. In winter, I throw chunks of it to the chickens. My austrian winter peas are four inches tall -- as tall as they will get until spring. Favas are not winter hardy for me, so I use austrian winter peas instead. The tendrils are good eating, but I pull the plants and compost them just as they start blooming in late spring.

A few years ago harry vetch was all the rage. I don't recall reading about it recently.

Ralph I can't say if it is too late in your part of zone 6 or not but it isn't here in my part. We just planted a mix of turnips and radish in several beds middle of the past week. Normally they will do well into mid to late January and we till them in then weather permitting.

Two of the other garden beds get planted with various deer fodder crops - winter peas, clover, chicory.etc. and all work well for green manures.

Dave