Check out MagnicLight. It mounts to the brakes, and doesn't use spoke magnets, but uses the eddy current that the spinning rim generates with the internal magnets in the unit itself. It is completely self contained. It also is removable so that you don't leave it out all night. The latest version will blink, since the US market demands that, while those sold in Germany can be disabled from blinking. This version also has a stand light and is also super bright.

Don't expect to be able to buy one just yet though. The guy making them is having some trouble getting them out to his Kickstarter backers at this point, something about getting the proper magnets to use inside the unit. I'm hoping he's successful, since I put my money into it.