I had this idea a few days ago and thought they'd be fun to make. These are round ornaments that light up and one has the Batman logo on it and the other has Gears of War. You can light them with any color and in a couple different ways. The video explains a bit more and shows them lighting up.
I've included a couple different options for the bottom part. There is a normal bottom that is just round with no features. The one titled "string-light-bottom" has a whole in the bottom that allows a string light (like christmas lights) to be inserted and will light up the clear PLA (see the Batman image above). Then the one titled "switch-bottom" is designed if you want to put an LED in there and half it be able to be turned off to preserve the battery. With the LED you can just get a coin cell battery and attach them (a resistor is recommended but not necessary). A little soldering is necessary if you choose to use the switch though.