After trying out various designs over the last couple of months (check out my other Instructables), I finally came up with this one. Inspired by the Led Earring instructable, I ended up using magnets to hold a coin cell battery and act as contacts for the LED. The cool part is that the battery actually serves as a switch - slide it up to turn on the light, push it down to turn it off. And as a bonus - you do not need a screwdriver to pull out the battery (as opposed to SMD battery holders).
I made about 15 such pendants and gifted them in the last Burning Man (2013). It was a blast :)
Short warning - I did not have direct access to a laser cutter at the time, so this design is not perfect. You'll need to make small adjustments to the parts you cut, so make some extra parts. Just in case.
Also, note that the pendant is asymmetrical.So make sure you align all the parts properly before cutting and gluing. I guess next time I should add "up" and "down" engravings on the pieces themselves.