You might have thought the barrage of municipal bond exchange-traded funds was over. After all, things have been pretty quiet lately, with the most recent launch taking place about a month ago. But, as of today, you'd be wrong, as Van Eck Global, a latecomer to the field, launched its second muni bond ETF.

The Market Vectors-Lehman Brothers AMT-Free Long Municipal Index ETF (AMEX: MLN) tracks the Lehman Brothers AMT-Free Long Continuous Municipal Index. The index is weighted by market value and includes fixed-rate, investment-grade municipal bonds with durations of at least 17 years and outstanding par values of at least $7 million. As implied by the index's name, its components are all exempt from the alternative minimum tax.

MLN carries a net expense ratio of 0.24%. The PowerShares Insured National Municipal Bond Portfolio (AMEX: PZA) also tracks long maturity muni bonds; it charges an expense ratio of 0.28%.

The new ETF joins the Market Vectors-Lehman Brothers AMT-Free Intermediate Municipal Index ETF (AMEX: ITM), which was launched December 6 and tracks the Lehman Brothers AMT-Free Intermediate Municipal Index. The components of the intermediate index have a nominal maturity of six to 17 years.

Actually, things are far from over: Another four muni bond ETFs from Van Eck are on the way, according to a registration statement filed by the firm. Still to come are a national short-term muni bond fund, funds covering the New York and California muni bond markets, and a high-yield fund. Should Van Eck launch all of the proposed ETFs as planned, there is a good chance it will have the broadest offering of municipal bond ETFs at one firm.

You can view the prospectus for MLN here.