Obviously the D20: it can roll 1-20, 1-10, 1-5 and 1-2 with ease. If you've got a quick enough wit, it can even roll 1-4.
Combine it with another D20 and it can also roll 1-8, 1-40, 1-80 or 1-100.
And that's only if you always use every face. If you are willing to go with "roll again" faces, it can roll a 1-6 (and thus 1-12 with another D20).
It's basically the perfect die. And it's a platonic solid. And if it's made by Lou Zocchi... ah, the glory!