Corn has almost quadrupled in price in nominal terms since 2000. In July of 2000 corn was making lows of around $75/ metric ton with highs for the year up around $95/ton. In August of 2011 corn was selling for over $310 a ton. Roughly from 3 to 4 times as much. Obviously , corn is volatile if it can move 30% in a few months. This can be due to weather conditions causing crop failures or other external factors.
There has been speculation that the recent dramatic increase in the price of corn is the result of ethanol becoming part of the gasoline mix.
But obviously that is only part of the equation. The real question is, "What is the price of corn in real (inflation adjusted) terms.
In the chart below, the black line represents the nominal (or actual price) per ton of corn since 1981. As you can see the nominal price stayed between $75 and $150 up until 2006. The only exception was a couple of months during 1996 when prices spiked up to $200. From 2006 onward however, prices have been climbing and haven't gone below $150 a ton. One of the reasons given for this "floor" under the price of corn is the increased demand from ethanol producers who use it to produce a gasoline additive / alternative.