Dow Transports - biggest single-day loss in ~5 months (2nd worst in 11 months)
Nasdaq - 2nd worst day in 10 months
AAPL - worst day in 3 months (2nd worst day of 2013)
USDJPY - biggest gain in JPY in 10 weeks
WTI - biggest single-day gain in 10 months
Financials - worst day in 10 months
In no particular order: Weak (and strong) US data (good or bad news?), War, Taper (Treasuries 'special'), Debt Ceiling, German elections, New Fed Chairman, imploding developing markets and collapsing global currencies... (S&P 500's first close <100DMA in 2013) it is on...