The Intermarket analysis chapters in John Murphy's The Visual Investor is worth a re-reading. Murphy's says commodity prices are usually a good leading indicator of stock market turns, since commodities are the raw materials that feed into the economic cycle. Higher commodity prices mean lower stock prices because higher commodity prices squeeze profits.
Right now Investor's Business Daily shows crude oil, heating oil, and gasoline going up. Gold looks like its topping, but that might be a temporary stall before going higher. And the Commodity Rearch Bureau Index looks like it might be heading up again.
Just my .02