The mixture I've settled on for summer is Hutchinson Soybeans (a forage soybean, i.e. produces a lot of leaves and can handle heavy browse pressure), Iron and Clay Cowpeas, and Buckwheat. Deer don't use the Buckwheat much during early to mid-summer, but pound it in August and September. The Cowpeas go fast as soon as they're up and the soybeans fill in the middle of the summer. I will hit the plot with the grass-killer Clethodim about 3 to 4 weeks after planting.
I added Black Oil Sunflower last year, but the deer ate it all too quick. So, I'm not adding that this year.