There is an interesting puzzle that has been listed on the front page of MathPuzzle.com that was made by Chris Lusby Taylor.

Simply place the numbers 1-9 in each cell, so that no cell has the same number as any other cell on any of it's 6 planes (wx, wy, wz, xy, xz, yz).

His puzzle has just 10 clues. My question is, can you make a puzzle with only 9?