Sure September is the worst month on average for the markets (see stats here), but September 2008 was one for the history books. The S&P 500 started the month at 1283, but within the weeks that followed, the markets saw Lehman Brothers collapse and the S&P hit a low of 1106 by September 29, a drop of nearly 14%. The Dow saw its biggest one day point drop in history, falling 778 on Sept 29. The CBOE Volatility Index rose from 20.65 on August 31 to 46.72 on September 29.
Financials, and particularly brokerages, tumbled along with Lehman's demise. Goldman Sachs fell ~50% from its Sept high to its low of the month while Morgan Stanley saw its share price fall by nearly 70% over the same period.
Here's a broad look at how things have changed going into the volatile month of September today compared to one year ago.