The SPDR S&P 500 ETF Trust (NYSEArca: SPY), PowerShares QQQ ETF (NasdaqGS: QQQ) and the iShares Russell 2000 ETF (NYSEArca: IWM) are three of the largest and most heavily traded US-listed ETFs. As such, IWM, QQQ and SPY also have some of the most robust options activity among US-listed ETFs,...