The classic Rubik's cube is available in different configurations, such as 2x2 pocket cube, the standard 3x3, and the more difficult 4x4 Rubik's revenge, and the 5x5 professor's cube. Yes, there are more difficult ones, too.
1. Grayscale Rubik's Cube
The Grayscale Rubik's cube is the same as the standard 3x3, but without the bright contrasting colors. The sides are different shades, but just barely! The moves are the same, but difficult because of the extra concentration required in distinguishing the colors.
2. Photo Rubik's Cube
You can have a personalized Rubik's cube made from six photographs. Each photo will be sliced into nine squares. This will make it hard for anyone who isn't familiar with the photos to solve it, so if you've never solved one, there's a chance someone else might mess it up for you. And cubes that must have all squares lined up in a certain orientation are more difficult, as they have a thousand times more possible configurations.
3. Rubik's Cube Earth
This is cool. The basic Rubik's cube with a map of the earth printed on it. Even if you're a cube quiz, you have to have some basic idea of geography to solve this. And it's a great conversation starter.
4. Magnetic Dice Cube
When I first saw this, I thought it was awesomely retro to make a Rubik's cube from even older gaming cubes, but that's not all there is to it. This dice cube is held together by magnets instead of the Rubik's mechanism! If you can't solve it, you can easily take it apart.
Sudoku is one type of puzzle I deliberately avoided learning to do, for fear it would suck up all my time. But if you know a Sudoku enthusiast, they'd have a ball with the Sudokube.
6. Fentix Cube
Andrew Fentem designed this electronic touch-sensitive cube to emulate a Rubik's Cube. It's as much art as it is a game!
The Megaminx is shaped like a desk calendar paperweight, with 12 sides. It has 50 moveable pieces, compared to 20- on a standard Rubik's cube.