The next Centennial Challenge competition will be the Personal Air Vehicle Challenge, which is coming in August. There is a lot to this Challenge, and it's all there - challenge rules, updates to the rules, rationale for the challenge, and more - on the CAFE Foundation site I linked, so for now I'll leave it at that. Expect more as the challenge date approaches!
For those who aren't already familiar with the Personal Air Vehicle (PAV) concept, or with the PAV Challenge, probably the best way to ease yourself into it is by taking a few minutes and watching this entertaining video on the challenge made for the 2006 Oshkosh Air Show (which I wanted to go to but missed).