There's a few more instruments on my page here built using 2X4s over the years. Here's a couple more in progress now (coincidence the 2X4 challenge).
6 string headless travel guitar, one 2X4, razor blade and small brush to make it look like a separate fretboard.
And the Mini Taser
OOPS, I'll upload better progress pics of Tesla later, forgot to dl from camera.
But you get the idea of what you can create from a 2X4