The U.S. and global stock markets climbed the proverbial "wall of worry" -- typical of bull markets -- in a year that will be remembered for the eurozone and Japan falling back into recession, slowing growth in China, central bank stimulus around the world, the U.S. fiscal cliff debate, record-low interest rates and worst of all -- the Twinkie's untimely demise. The world's largest ETF, SPDR S&P 500 (SPY), returned a handsome 13.56% in 2012.