Lady Ada tells me that there's an interesting new material that's been developed. It is an alloy that develops a magnetic field in proportion to its temperature. There are some immediate implications to this, most startlingly that it is now possible to turn heat into electricity.
This produces electricity because electricity is produced by a varying magnetic field near a loop of copper wire. Traditional power plants use a spinning magnet -- the wire is exposed to different magnetic fields as the magnet turns. This system would instead produce a magnetic field that changed as the temperature did. As it heats up, the field gets stronger, and as it cools off, the field gets weaker. So if you left it in the sun, it would start to heat up starting a little after dawn, until sunset, when it would be quite hot indeed. After dark, it would cool off. Cyclically, this would produce power, over a longer frame than solar cells because there are no moving parts.
However, the sun isn't the only thing that heats this thing up. You could use car exhaust, fire, nuclear waste, or in colder climates, even just grabbing it periodically. (Less than pleasant, though). The possibilities are literally endless, as heat is the most entropic form of energy, therefore almost all energy-using processes will produce heat. And now that heat can give you some of its energy back as electricity.