Algae Research
This is interesting: Exxon Mobil is planning on investing $600 million in producing liquid transportation fuels from algae, according to this article in the NYT. The potential energy yield is significant, especially compared to corn (2,000 gallons of fuel per acre of production each year, compared to 250 gallons per acre a year).
[Update: The WSJ has an article briefly discussing this and other algae projects. Interesting. (Note - Subscription required.).]