State Street (STT) looks to take on iShares' (BLK) dominant small cap ETF (IWM) with the Tuesday launch of the SPDR Russell 2000 ETF (TWOK). IWM currently has $23.3B in AUM and an expense ratio of 0.24%. This compares to other far smaller competitors like Schwab's SCHA at 0.08% and Vanguard's VB at 0.10%. Previous: Small cap stocks outpace the S&P 500. Other reasonably popular ETFs: IJS, IJR.