First there is the Lucetta Magnetic Light. We really love the small form factor and the way it works, but check the video …

And for the rainy days in we got the Fendor Bendor 3. A lightweight foldable fender that will fit the back pocket of your cycling jersey.

Lucetta Magnetic Light: 25 EUR for a set.
Fendor Bendor 3: 15 EUR.