shadow. you are correct that peas/beans are a great "bonus" food plot. The deer will eat the foliage though out the growing period and then eat the pods in the Winter. One thing that you have to keep in mind is, once the deer eat them down, they are gone. They don't take very well to heavy browsing. So, usually if your plot is less than an acre in size, the deer will eat them down to nothing as soon as they start coming up. I have seen a small plot of peas/beans do fairly well in small plots but the deer usually had something else in the area they were eating too. This took some of the pressure off of the beans. Also, cow peas do not grow well after it gets warm. They are cool season peas which is why some refer to them as Winter peas. But, this may work well with the warms season soy beans.
As far as clovers go, there are several different verities and they grow in different stages. Some are annuals, meaning they have to be reseeded every year. If you cut them at the right time of year, when the blooms are at head, they will reseed themselves to an extent. Some are perennials, meaning that they work off of a root system. These still need to be clipped a few times a year to keep the tender growth coming, but they react well to clipping and heavy browsing. As long as you keep the tender sprouts coming the deer will eat it on a regular basis. In the Winter, they do go dormant as far as growth, but the dormant plants still offer great nutritional value to the deer. They will seek these plots out in the dead of Winter. I have about 3 acres of clover in 4 different plots. The deer are really using them hard right now. This is a plot that they will dig through the snow to get to. Also, the clovers are much more labor friendly than most other plots you could have. Once they take hold, they are very easy to maintain.
I have about 15 acres of soybeans in 3 different plots. They served their purpose, but are pretty much done as far as having anything to offer the deer now. They used them during the Spring, Summer and early Fall and then again this Winter, but it didn't take them very long to eat what was left as far as bean pods go.
I don't really know if there is such a plant that will offer the deer what they need at all times of the year. Most plots have to be rotated from Spring to Fall to offer the tonnage and nutrition that deer need at specific times of year. If I had to choose one that closely falls into that category, I would say clover. But hey, try anything once. If it works, stick with it. If it doesn't, try something new.
It might be more cost efficient to go with the "buck-in-a-bag" seed mixtures if you are only doing one smallish plot. If you are planning on doing more than that, do yourself a favor and go buy you a bag of cow peas/iron clay peas and a bag of soy beans. You will pay just a little more for alot more seed.
That's just my two cents worth with several mistakes made in my learning curve.
Hunt as though your life depended on it, because one day it just might!