Here is a link to a powerpoint presentation that includes these charts:
March 2008 USDA Planting Intentions
Here are some charts from the presentation. For some rather amazing conclusions about the long-term prospects for grains as an investment, look at the entire presentation, especially the conclusions at the end. Here are the sample charts:
Corn -- Stocks at 30 year lows
Soybeans - Stocks at 30 year lows
Wheat -- Stocks at 60 year lows
US Dollar - Longer-term perspective
The influence of investors and funds