If you have farmland, any of these vegetables might supplement your income if you find the right loyal market nearby. My favorite idea which I've mentioned here in the past is asparagus, or purple asparagus. Here in Colorado where the climate is tough, one innovative farmer provides all of the varieties of rhubarb and horseradish to locals as U-pick.
These unique ideas morph into tourist attractions, too, since the bored masses are always looking for something out of the ordinary.
source: USDA