From the best international blogger I know comes a list of "ten most influential courts in the modern world." He caveats,

As always with these lists, the things that make a court "influential" are partly in the eye of the beholder. My rankings were based on a non-exhaustive list of characteristics including influence on their own countries' law, influence on law elsewhere in the world, development of legal concepts, courage in maintaining the rule of law or applying it under difficult situations, and presence of important legal thinkers: take them for what they're worth.

In order, they are: International Court of Justice, European Court of Human Rights, SCOTUS, Judicial Committee of the Privy Council (of which, to be honest, I'd never heard before now), South African Constitutional Court, Supreme Court of Israel, Hungarian Constitutional Court, Egyptian Court of Cassation, High Court of Australia and Supreme Court of Canada.