Vetch is one that comes to mind as far as a quick working nitrogen fixer that also easily reseeds itself. You may also want to try alfalfa which will hold up pretty good once it's established. Of course clover as you mentioned.
With bush beans I would wait til they produce their crop, then chop the plant to the ground after you harvest.
I like using field peas in clumps. They grow up about 4 feet tall and -if planted densely enough- will support themselves with no trouble at all. They make good animal feed and you can dry the peas for winter storage. Split pea soup and the like.
Comfrey will just about take over after one chop. It comes back so fast that it ends up shading other low growers out. You may want to think about leaving plenty of space between comfrey plants to allow other things to have a chance. My comfrey spreads about 2 feet from root to leaf tip horizontally and grow three feet high in a few weeks. I chop it 4 times a year.
You could also look into nitrogen fixing shrubs and trees to accompany your other plantings. Siberian pea shrub is nice, hardy, prolific with flowers and seeds which are edible though probably better as animal feed. Wild things like Autumn Olive is pretty nice too. It grows fast, fixes lots of nitrogen and produces a berry which can be used for making jams and juices. It's similar in taste to tomato though each shrub varies in it's flavor. I have many of them on my land and I just cut out the ones that don't taste so great and feed them to the animals. The pigs like the leaves and fruit while chickens will only eat the fruits. Sometimes they come back from a total cut-down, but in most cases it seems like a new seedling will show up somewhere within 30 feet of the old shrub.