I have a short letter in the November 2009 issue of Nature Biotechnology (subscription req.) correcting the record on US revenues from genetically modified crops. Based on USDA data for corn, soy, and cotton, revenues from the GM versions of those crops were about US$ 65 billion in 2008, rather than the widely misreported ~$4 billion. The latter figure is in fact just from GM seed revenue. I would put the total from all GM crops and seeds at $75-85 billion, though it isn't yet clear where GM sugar beets are going to come in. Assuming US revenues are representative of global averages, thentotal worldwide revenues are probably north of $150 billion for crops and seeds together.
Below is a figure showing US yearly revenues from the three big crops, as well as the US annual total. Note that although the GM fraction of each crop continues to grow (see the ISAAA report from 2008), prices fluctuate sufficiently from year to year that total revenues declined from 2007 to 2008. Food and crop prices have come off their 2007 highs -- which cannot last given increasing demand around the world. I would expect revenues to resume their climb in 2010.