I've been using a mix, from a local feed store, that consists of 50 % Corn and 50 % soy bean in my feeders for 3 or 4 years. I like it because the corn has very little protein (mostly fat) and the soy bean is 18 to 20 % protein.
They won't hardly eat the soy bean for a few days, but after a while they will eat it just fine. Seems to make quite a bit of difference in the health of the deer I have on the lease, versus corn alone. I see a weight gain of about 10 or 20 pounds on yearlings that are raised on it, and most of the first year racks are generally 4 points instead of spikes.
The mix works well together through a spin feeder or a straight shot feeder, and won't clog up in humid weather.