Another thing i'm toying with is playing the immense volatility on oilprice and natgas prices with those 3x leveraged bull/bear ETNs/ETFs-- like UWTI/DWTI and UGAZ/DGAZ.
CAVEAT: these are NOT (NOT! NOT!) long-term "buy and hold" "investments" (because of the terrible "decay" over time of their share-prices) but rather short-term instruments for swing-trading the rising/falling commodity prices.