Vanguard provides VGTSX (Total International), which attempts to invest in non-US markets in a balanced and diversified manner. I consider an international fund crucial to maintaining diversification, though many people feel it's too volatile. It was the only thing I found in all my reading where people had widely varying opinions with no true consensus, in which case you should go with your risk tolerance.
I have often benefited from recommendations for Things I Didn't Know I Wanted.
Given that Less Wrong is a community of unusually intelligent, critical, and self-improvement-focused people, I suspect we can generate a pretty helpful thread of product recommendations — perhaps even a monthly thread of product recommendations.
Rules: