Many years ago (sometime around 2001) when I was just starting to make puzzles with a 3D printer, I experimented with a few burr designs. One of them was Peter Marineau's Piston Puzzle Burr. I recently decided to revise the model a bit for the Shapeways process, so I'm also making it available to you.
You can buy the puzzle for under $20 in my Shapeways shop
Here are a couple photos of the puzzle in blue and purple:
Purple Burr Solved.JPG [ 185.27 KiB | Viewed 408 times ]
Blue Burr Pieces.JPG [ 193.4 KiB | Viewed 408 times ]