We have all heard the old Wall Street adage to “sell in May and go away” until October, as the market historically underperforms in the May-September timeframe. And indeed, after the “bin Laden gap up” at the open on Monday, stocks quickly turned tail. Today, the selling intensified following the disappointing ISM Non-Manufacturing Index for April, with Energy and Materials the hardest hit.

For the first time in the 98-year history of the Federal Reserve, its chairman held a news conference after its FOMC policy meeting. So, what was the big news? QE2 will end in June as planned, but as I speculated last week, they will keep the balance sheet steady by continuing to reinvest maturing assets into the debt markets. They will also keep the Fed Feds Rate in the 0.00-0.25% range. Both of these are stimulative to the economy.

In my weekend analysis, I talked about the possibility of a bullish reverse head-and-shoulders formation for the stock market. And after allowing for a brief panic on Monday, the market has been quite strong this week and appears to be confirming the bullish pattern.

Last week I mentioned that a pullback was due, and indeed we’ve seen some market weakness this week. The 50-day simple moving average is trying to support the large, mid, and small caps at this point, but the Dow Industrials and MSCI Emerging Markets are holding up better as they are supported by their 20-day. Among the major sectors, Healthcare has actually displayed strength this week despite overall market weakness.

Although trading volume remains anemic, with NYSE volume below 900 million today, equity bulls continue to run the show as the global “wall of worry” seems to suit them just fine, thank you.

Bulls continue to shake off global challenges to keep the market in rally mode heading into the end of the first quarter, led by powerhouse sectors Basic Materials and Energy as well as Healthcare and upstart Telecom. In fact, the S&P 500 is on track to achieve its largest first quarter return since 1998. The SPY closed today at 132.77, up 5.6% on the quarter with one more trading day to go.

Market bulls found support at the right time and pulled another rabbit out of their hat. It’s good to have friends in high places, as the Fed’s POMO money continues to flow, including another $6+ billion today for the purchase of Treasuries (which tends to find its way into equities). Last Wednesday, I suggested that the extreme weakness might have been a selling climax, and it turns out that is was – at least for the short term.

Last week I wrote about the market’s impressive run off the March 2009 V-bottom. But since then, the bottom has fallen out, led by the Technology sector. Those of you who read this column regularly know that I have been opining that the rally has been pretty much manufactured by the Fed and their quantitative easing initiatives, but more recently the signs of economic recovery have been taking shape without much inflation.

Today marks the two-year anniversary of the V-bottom that launched an impressive bull market. Since then, the SPY large cap is up about 95%, while MDY mid cap and IWM small cap are up about 135%. Leading sectors include Basic Materials, Industrials, and Financials, which are each up at least 150%. Pretty impressive.