Depends on the time of the year.

Soybeans are great for the summer, but once beans mature they must get bitter, because the deer leave the beanfields and head for the corn.

Corn, either standing or picked, will hold deer all fall and winter. There's always some corn left in the field after harvest, and like farm hunter said, standing corn will be available in heavy snow.

Forage crops are good spring, summer, and fall. As long as there are nice tender greens, the deer will be there. They will even paw through light snow to get to it if they know it's there.