Over the past six weeks, we’ve talked about the ETFs that make up my top seven list for 2011. Today, we conclude our series, and this time it’s all about a bet against bonds. But before we dig into the details of this week’s offering, let’s recap our first six ETFs.

Part I in our series highlighted the SPDR S&P Oil & Gas Exploration (XOP), while Part II featured the Market Vectors Agribusiness ETF (MOO). Part III profiled the Technology Select Sector SPDR (XLK), and Part IV covered the metals and mining stocks ETF, the Market Vectors Gold Miners ETF (GDX). Part V in our series showcased the ProShares Ultra Dow 30 Fund (DDM), and Part VI gave a snapshot of the ProShares UltraShort Euro (EUO).

Part VII introduces you to the ProShares UltraShort 20+ Year Treasury (TBT).

This fund is basically a leveraged bet against the price of long-term Treasury bonds. Another way to put it is that TBT is a 2-beta bet on rising interest rates. The fund seeks daily investment results, before fees and expenses and interest income earned on cash and financial instruments, which correspond to twice the inverse of the daily performance of the Barclays Capital 20+ Year U.S. Treasury Bond Index. So, if long-term Treasury bond prices fall 2%, TBT should climb 4%.

As you can see by the chart here of TBT, the fund exploded in September and essentially kept climbing until mid-February. That’s when the selling in stocks began, and that’s when investors started warming up again to bonds. The traditional “flight to quality” that we see in Treasuries as a result of global unrest or natural disaster (this time both) has caused money to pour into Treasury bonds during the past week. Due to the inverse relationship of TBT to bond prices, the fund has fallen sharply. TBT now trades below both its short-term, 50-day and long-term, 200-day moving averages.

I suspect that once the fear in the market has subsided, TBT will return to its winning ways. For short-term investors and traders, the technical move below key trend lines could mean a new buying opportunity in TBT as it begins a rebound. I don’t think this fund is a buy just yet; however, I do think once the dust settles, TBT once again will look extremely attractive.