[nate_martin]

Technically I think you could make any n-sided die for even n > 2:

1) Take an n-gon cylinder.

2) Smooth off the two ends to be spherical so that it never lands on either.

Now all sides have equal probability of facing up after a roll.

[carstimon]

You can even make it polygonal. Even more interesting, you can make it non symmetrical, contradicting the article's claim that dice must be symmetrical to be fair.

You make an (n-2)-gon cylinder. This has n faces (the sides, the top, and the bottom). If you make the top and bottom very small, the probability of landing on them is smaller than the probability of landing on the sides. If you make the top and bottom huge (compared to the sides) the probability of landing on a side is smaller. Somewhere in the middle, the probabilities are balanced.