Over at Instructables, contributor Handsome Ryan has an excellent guide to mounting LED lights in your bar ends. The lights are switched on via magnet attached to your bike glove.
This is a great bike hack for commuters. We commuters have already got enough lights to think about turning on and off every time we hop on the ride--two automatic lights that increase side visibility would be great! This hack looks like it takes a few less common items that you might have to source on teh internets rather than locally. But it's all pretty cheap.
If you're anything like me, you should probably set aside a full half day to get these things running. I'd probably put 'em on upside down first, then backwards the next time, before finally getting it right.
On a side note, Ryan is responsible for quite a few posts on Bike Hacks. Spin the wheel to win.