Great picture comparing the price of the 3 main energy options: coal, nat gas, and oil. Not only does this chart show current prices, but also the futures for each item.
It is worth noting the higher prices of natural gas in the future. The price increases substantially over current prices. Unless coal sees a similar rise in the future, all the power stations converting to nat gas will cause higher utility prices down the road. Especially in case where coal plants are being closed. Maybe great for the environment, but I seriously doubt consumers will agree when they get bills during a brutally cold 2013 winter. Just guessing.