I got one of these chinese solar rechargable keychain lights last christmas from my brother.
Originally the light uses an LR2032 which is a rechargable lithium version of a traditional CR2032 button cell.
I had an ultracapacitor I ordered from Farnell for the heck of it left over that I didn't really have any plans for along with some higher power (though smaller) LEDs. The result is what you see below.
I also changed the blocking diode to a schottky so that the ultracap charges to a somewhat higher voltage.
It supplies a good amount of light for a reasonable time. I keep it under a light source (on top of my water heater next to a light bulb) so it's always ready in case of a powerout. (I can easily get to the water heater in complete darkness from anywhere) It's come in useful a number of time already :) Not really worth the price of the ultracap though but whatever...