The CAFE Foundation, the organization that runs NASA's Personal Air Vehicle Centennial Challenge, plans to start a Green Prize part of the 2008 PAV Challenge. Their announcement is currently at the top of their main page:
CAFE creating "Green Prize"
The CAFE Foundation, respecting the ever increasing concerns about energy and global warming, is planning to launch the "Green Prize" as a main part of the 2008 PAV Challenge. The Green Prize will seek a corporate name sponsor and will reward outstanding fuel economy and use of renewable fuel. Watch here for more news about it soon.
Anyone who has followed the airline industry news in the last couple years is aware that fuel economy and carbon emissions are major economic and regulatory issues for that industry. It makes sense for the PAV community to tackle them right from the beginning.
By the way, you can check the status of this (and other) Centennial Challenges at NASA's site here. You can see that the prize categories for 2008 are similar to the ones this year (with the addition of the Moon Regolith Oxygen Extraction Challenge), and the same allied organizations are running the prizes next year. Dates for the 2008 prizes are all TBD, though, including the PAV Challenge. The prize purses are, as planned, larger, as unwon and new amounts are combined.