This is an old article, but it's important enough to bring up again. Discover Magazine published an incredible article (a free version of the article is here) on turning waste into oil. The basic process is like oil refining, but with a first step that can effectively take extremely low grade oil in the form of ground up waste. While the US doesn't have a lot of crude oil these days, we have plenty of waste, so this technology could be a fairly big deal.
Update: A research team is trying to use the same technique to turn pig manure into oil.
Update: The first of these plants went online today (May 19, 2004), producing a few hundred barrels of oil a day from agriculture waste.