I got asked a question the other day, what I used in a frugal way to do ground cover and I have to admit that my big ones are pretty darn simple..
The first three are because I have tend to have whole grains available pretty much all the time for my feed, and it means if I turn and prepare the ground, I can sprinkle it down heavy in one of them, within a matter of days, its sprouted and it will come in hard and thick and give those weeds a huge run for their money, and its got great bio mass to cut, drop and plant over and or turn under depending on what I am doing.
The other common one is Raddish seed, its just so easy to grow, harvest and have jars of this seed on hand.. it could be called old faithful, but it can not be left as long, it needs to be turned quickly, as you do not want bulbs forming, so its a very fast turn around.
Then here is Mustard greens, I like growing them, not only easy to grow, you can take a harvest of baby greens off for a number of weeks without effecting overall growth, through in the bio mass when you cut and chop, but the big joy of using mustard is that it has a great effect on the soil but its a bug trapping crop! Just can not ask for more..