The S&P 500 continues to make new lows in after-hours trading. Right now, futures have fallen to levels around $1540 – down 2.6% on the day. This is the biggest sell-off in stocks of 2013 so far, and comes after weaker than expected economic data out of China, weak housing data in the United States this morning, and of course, a massive sell-off across the commodity complex, most notably in gold (which is down 10% today).