Philips has some fantastic new magnetic LED lights coming out at the end of this year that are perfect for the closet. Why the closet? Because they're magnetic, they're cordless, and they turn off by themselves after 15 seconds of not sensing any motion.
Other cool details: they cost between $10 and $15 each, and have a magnetic back that makes it easy to change its three AA batteries. The lights are really bright (thanks to the LEDs), are white (not blue), and will be available in silver first and other colors later. Hell, we didn't even know we needed motion sensing lights for our closet before this, but now we're on board.