Who would have thought that in 2006 you should have sold everything you had and bought... cooking grease!
That's right. According to the black market prices quoted in this SF Chronicle article, cooking grease went from being nearly worthless to now being worth 32 cents a pound.
Restaurant owners used to pour the stuff down the drain to avoid the proper and environmentally responsible disposal process. Now thieves are breaking into any barrels they can find to siphon the oils out and selling it on the black market, where it is coveted as a convertible biodiesel fuel.