Perplexus is a great educational toy which comes in a variety of different models and is suitable for children in the age range 6 to 14. In fact, adults will enjoy this as well.
It is, quite literally, a twist on a traditional toy. It's a 3D maze where the object is "simply" to get a small steel ball through the maze from start to finish.
It's a real brain teaser that will keep your kids (and you) entertained for hours on end.