Rekubus is another great puzzle that I recently discovered and was entered at the 2008 28th IPP Design Competition. It's an assembly (put together) puzzle and the goal is, of course, to make a cube with its 38 pieces. At first glance nothing extraordinary there, but if you have two or more cubes, the puzzle gains another dimension.
One of the possible challenges you can make with multiple cubes, is to swap pieces between them, making a wide range of these interesting patterns of contrast.
Another challenge is to create different structures, other than just a cube. This one gets really interesting when you have 4 or more cubes. You can create a bigger cube with four single cubes or you can also make a tower. There's no limit to what you can do with multiple Rekubus cubes.
The company makes several different solid color cubes and multiple colored ones, so you can choose which colors make the best contrast patterns. Besides the color cubes, it's also available a cube with numbers that have three difficulty levels.
Every cube costs €11.95 and you can find them here
(Click to Enlarge)