I like when you find a "kids toy" that appeals just as much to adults, if not more. In fact, I'm half tempted to add this to my own Christmas list - forget coffee table books, I'll take this as a coffee table toy!
Infinitely restackable, Dado cubes give kids a chance to learn about building, balance, volume and color gradation in an ever-changing format. The cubes catch the interests of a very wide age range, plus, whatever form they take, these are great left lying around as a modernist sculpture. They're even a fun size-match challenge to put away. Adults will find themselves reshaping their, ahem, abstract vision of utopia long after the kids have gone to bed.
Available in pink or blue.