Once you've learnt to solve the cube (or even if you are still learning) you can have a bit of fun with patterns. From the solved cube it is possible to make a series of interesting patterns. Figuring out how to create these patterns or getting someone else to create them and then seeing if you can turn them back into a solved cube without starting from scratch is an interesting and fun way to improve your understanding of the cube.
This is a rather nice looking pattern that is quite easy to create. There is a nice symmetry to the creation of the pattern. See if you can figure it out before looking up the algorithm.
This one is a little trickier to create but not by much. This one you can probably figure out intuitively as well. A good challenge to go at to help build your skill.
This one again looks rather elegant but now we're getting even trickier again to create. If you can create this one intuitively your cubing foo is definitely strong. If not, just look at the algorithm and go from there.
Look at the cube below. Can you see what we have done here? Each edge piece has been kept in place but flipped around. This creates a pattern which has the illusion of being scrambled but is done so in an organised way. The algorithm is quite large to create it but if you can remember and perform it without looking at the cube you can trick your friends into thinking you can solve the cube behind your back or with your eyes closed.
This algorithm, like Crosses and Diagonals, is nice in that you can perform the algorithm a second time to return the cube to its original state. You don't need to remember the algorithm in reverse as well.