Invest some of this cheap energy
I've tried to avoid predicting energy prices, except to say that they'll be volatile. I'm not a bit surprised to see oil and gasoline prices dropping by half in the past few months. I do think, though, that the long-term trend is up. If I'm right, you should seize this opportunity to invest some of this cheap energy for the long term.
The thing is, energy is hard to save. The most efficient system for storing electricity involves pumping water uphill so that it can run back down through a generator--not practical for your average homeowner. Storing gasoline in quantities beyond what fits in your car's tank is similarly tough--the stuff is toxic and explosive, plus it'll evaporate on you. Natural gas is even worse. (There is the bank of gasoline, but those sorts of schemes are all too prone to go bust in times of economic stress or spiking energy prices--i.e. just when you need them most.)
The solution is to use the energy to produce something of enduring value. Something that you do or make now with cheap energy won't have to be made or done later with expensive energy. If the thing you do or make actually produces or saves energy (putting up a windmill, say, or adding insulation to your house), so much the better.
If you own land, for example, this is a great chance to make the sort of change that's easy with cheap energy--digging ponds or ditches, building up berms, etc. A change to the contour of the land could be made now and last for generations. A solar power system could last for the rest of your life. A more-efficient furnace could last 20 years.
You're doing this in a small way anytime you buy something that will last. As you make such purchases, give some thought to what things have already become cheaper because of dropping energy prices, and remember which things shot up the most when energy prices were spiking. Those are good guides of where to focus.
If the economy were doing better, I'd point out that this is also a chance to just spend some energy. A winter road trip is going to be a lot cheaper than a summer one would have been. Airfares haven't come down much yet, but cheap fuel and a collapsing economy will likely mean a shot at low-cost flights. (It also means a shot at bankrupt airlines, so make sure your plans allow for that possibility.) As things are now, though, I can't really recommend just spending energy. Invest it.
Energy is likely to stay cheap for about as long as the economy is in recession. Energy that you can invest now, while it's cheap, is energy that you won't have to buy later, when it may be a lot more expensive.