The Evil Mad Scientists made garden party lights out of LEDs, lithium coin cell batteries, and mason jars. The result is very nice, especially when you consider how easy they are to make.
To start with, we need LEDs and lithium coin cells. One each per jar. The best kind of LED for this design is an ultrabright LED with a diffused lens so that the light cast by the LED chip goes in *every direction,* not just in the direction that the LED points (which is what you get with LEDs that have clear lenses). Having easy access, we opted for the 10 mm diffused white LEDs from here, but you can get similar LEDs elsewhere as well.