Besides the solar LED keychains, we've also gotten a few of the landscape LED lamps. Walmart had the cheap ones for as little as $2.50 USD each.
They are great to put out by the chicken coop, the path to the garden house, and all over. They work great as a handy flashlight.
They also seem to be helping the chickens to lay eggs better in the darkness of a Pacific NW spring. We've also noticed that the deer and chicken predators are also put off by the lights. That is good!
Besides all these handy uses there are some valuable 'guts' in the things.
A rechargable 1.2VDC battery, charging circuitry, and light detector (to switch on the light) are also inside - individually these parts would cost way more to buy from digikey.com...
Some of the ideas we've tried successfully: daisy-chaining a few of them together to use as an emergency charger for a cellphone (or USB device).
Two of these together work great to power a small, low-power PIC microcontroller (12F675 works fine) for remote applications.
They are simple and easy to hack - just cut the right wires.