You always hear about how you should change to compact fluorescent lightbulbs and turn out the lights when you leave the room; with something like Motionbulb you can have both at the same time. A slick motion sensor is embedded in the bulb's housing, turning itself on when it senses motion within 25 feet, and switching off when you leave the room.
Details are a bit sparse on their site, but the CFL-style bulbs do screw directly into conventional light sockets; the repeated on/off cycling might make these a better solution in an attic or other lightly-trafficked room, though each bulb carries a 5-year replacement warranty. If these were LED bulbs, we'd have a truckload on the way; as it is, Motionbulb could be an easy way to cut back on energy use and worry less about flipping the switch when leaving the room. ::Motionbulb