No till cover crops for the north?

I just read about cover crops in my latest Mother Earth News magazine and it got me wondering about ways to incorporate them in my garden.  I have 3' wide beds and I plant my early crops from mid April to June 1 and my warm season stuff in early June.  First frost is usually mid September.  

Questions:
1.  Is there a nitrogen fixing cover crop that would be worthwhile to plant in the beds where I'll be growing warm season crops?  I think they need to flower before they're killed in order for them to be worthwhile.  For reference, my earliest snap pea plantings are usually putting out edible pods by July 1.  Probably flowering the first to second week of July.  

2.  Is there a way to plant a cover crop of legumes that I can clear spots into for transplanting peppers and tomatoes?  They'd need to be short enough to let light get to the transplants so my normal snap peas would be way too tall.

3.  I'm afraid of planting clover since I want to be able to convert the bed to food production and not be fighting to eradicate the clover.  Are my fears unfounded?  Maybe with a kind of clover that winterkills here I'd be ok.

4.  I don't have any beds free until after first frost.  Then a number of beds become available.  I usually spread compost then and once the leaves start to fall I mulch the beds with chipped up leaves.  Maybe there's something in the cover crop department that I could do from mid Sep until Nov 1?

Musings:
A.  I used an Earthway seeder this year and had some beet seed get planted in a row of peas.  Once the peas were done and cut off at ground level, the random beets were discovered and were a few inches tall.  With full sun they have grown nicely and may put on a proper root yet this year.  I'm thinking I could deliberately do this in the future by planting a triple row of peas with a row of beets between each row.  Once the peas come out the beets can get into gear.

B.  I think I'll grow a bunch of cabbage starts next summer so that I can transplant them into the garlic beds when the garlic comes out in mid July.  Hopefully I'll get a crop from them before it gets too cold.

White clover  is not that hard to rake out of a bed and compost. Crimson clover will probably winter kill.  I aim for more useful planting winter hardy kale among the declining plants in late summer. these survife frost and evem under snow and give me a harvest in spring before last frost.  I have saved a lot of seed if you would like some.

Thanks Hans, PM is on the way

You know, chickweed is a nuisance here. But if I could seed chickweed late enough, it would generate a ton of veggie matter without forming seed. Hmm...

Not really a cover crop but I also realized I can plant cut and come again greens in a bed that will turn to peas later in the early summer

I would not put white clover anywhere near annual planting, it's very invasive and will grow/straggle up at least a foot in height. It spreads by runners so does not like staying where you put it.  and the type we have here is hard to pull out again! I have it between my strawberry rows and it does fine there but it is sandwiched between plastic ground cover and the lawnmower. even then it does try to invade the strawberries.
If you can't plant until after the first frost you're not going to get a good cover crop no matter what you plant. you might be better off planting something somewhere else and then using it as mulch. But you could plant your cover crop a few weeks earlier around the plants in the beds.