I don't think any of them will double, but I think that corn has the chance of moving the highest percent wise. Here is my reasoning:
Wheat fundamentals are horrible...too much non-US production right now, so the battle is between beans and corn.
With the cost of inputs rising dramatically (fertilizer, herbicide, etc) farmers are likely to opt for the less input intensive soybean over the VERY input intensive corn. Added to this is the fact that with the last two years higher corn acreage, most of the ground this year would be corn behind corn again (2nd year in a row for this), which would require even more nitrogen inputs (nitrogen up 30% from last spring already). The acre war will increase the price for both corn and beans, as beans will have to keep up, but I think that in the end, farmers will not want to pony up the extra expense on corn, simply from a risk management standpoint. (crop insurance still sucks if you look at the coverage). Also, I don't know how the credit situation will shake out, but if lending gets tightened at all in the farm sector, you can bet for sure more beans will be planted. My analysis is targeting $7 corn for next year, while only seeing $12-14 beans (top end on both...but its a ways off so who knows)....so the percentage move is definitely in favor of corn. Am I off base here??