Over the past four weeks, we’ve talked about the ETFs that make up my top-seven list for 2011. Today, we continue with our series, and this time it’s all about doubling down on the Dow. But before we dig into the details of this week’s offering, let’s recap our first four ETFs.

Part I in our series was the SPDR S&P Oil & Gas Exploration (XOP), while Part II was the Market Vectors Agribusiness ETF (MOO). Part III was the Technology Select Sector SPDR (XLK), and Part IV was the metals and mining stocks ETF, the Market Vector Gold Miners ETF (GDX).

Part V in our series is the ProShares Ultra Dow 30 Fund (DDM).

This fund is a bullish, speculative play on the upside potential of the Dow Jones Industrial Average. This is not a fund for newbie investors, or for those who don’t have much risk tolerance when it comes to their capital. That’s because DDM is a fund designed to deliver twice the daily performance, less fees and expenses, of the Dow Jones Industrial Average. So, if the Dow rises 2% in a day, DDM should climb about 4%.

Now, assuming the current pullback in stocks is just that, a pullback, then this market is liable to really start running higher again once the selling subsides. If this happens, then a leveraged bet on the most widely followed stock index certainly will deliver some very healthy profits.

This is the kind of ETF that I would use in my ETF Trader advisory service, as that service is designed for more aggressive traders. With DDM, a market bull can really be a market bull.