The S&P 500

The S&P 500 is more than 20% off its March 6 low, and has taken out key resistance levels, Brown Brothers Harriman notes; the next key is the "double top," firm says. "The next significant challenge will be breaking the late-January and February double top around 870 as well as the downtrend line drawn off the failed rally peaks of October, November and January," firm writes. On the downside, 760 and 745 are the 38.2% and 50% Fibonacci retracement levels of the rally through Monday's high, and will be important support to hold when the first real pullback sets in."