SPY (S&P 500 Index ETF) -- currently at 89, has fairly big May open interest at the 90 and 85 strikes. About 211k open interest at the SPY May 90 strike, about 292k open interest at the SPY May 85 strike. 90 seems the likely area to me at this point if we do end up getting pinned close to a strike price. 900 is also a key technical level on the S&P 500 Index.