Undoubtedly the most well-known, and most traded, asset correlation is that between the U.S. dollar and gold. This is a negative correlation that sees gold rise when the USD falls, and vice versa. The reason for this correlation is that gold is priced in USD, so when the USD strengthens gold becomes more expensive outside the U.S. and demand (and thus price) drops. That doesn't mean you can trade this correlation blindly however. As with most correlations it is not 100% and at times gold and the USD are positively correlated, or show no correlation.