Mi-Mi Moscow / Dada Arrigoni
If you have even half a teaspoon of interest in conceptual art jewellery, you'll already know the name Mi-Mi Moscow (Russians Mila Kalnitskaya and Micha Maslennikov). Whether you're visiting them for the first or fifteenth time, their site is always worth the visit.
Below, a ring from their much-lauded frog series:
Even more jewellery: