The municipal bond market hasn't provided standout returns lately. Unless you are in a top tax bracket and buy a long-term muni—which comes with a lot of interest-rate risk—yields on an after-tax basis aren't much more than Treasuries. The largest muni index fund, the $42 billion iShares National Muni Bond exchange-traded fund, yields 3.3%, equal to about 5% for a taxable bond fund. ...