The number one issue with bike lights is the fact that they're easily stolen, a fact that has caused many bike light manufacturers to designing them as cheaply and disposable as possible. However, a group of two engineers and an industrial designer in Brooklyn are taking an inverse approach with their pricey, aluminum Blink/Steady bike light.
The Blink/Steady solves just about every problem you've ever likely encountered with a bike light(like having to turn it on/off) by using an accelerometer and light sensor to turn and keep itself on at night and off in the daytime. The issue of being stolen is easily enough resolved by the fact that the light screws right onto your seatpost.
Help these guys get their idea into production with support on their Kickstarter page and for a donation of $95 or more you can have one pre-ordered. That may be a bit steep for a bike light, but you're likely to never have to buy another one again, it's that good.