I liked thing:952547 (http://www.thingiverse.com/thing:952547), but didn't have any transparent ABS. So I used my CNC router to cut the pyramid out of an old CD case.

http://www.youtube.com/watch?v=UuvrFF7oMA0

Cut 4 identical pyramid faces out of a transparent CD case.
Print the top and the bottom parts.
Snap everything into place.
No glue is required.