Muni bond with monoliner insurance, 4-4.8 percent yield and federal tax free
, pay interest every 6 month. If you consider zero coupon bond (no interest,
return you face value till maturity, you pay 45-48$ for 100$ face value as
15 year mature bond), the yield can be higher as 5-5.5 percent. If you buy a
muni of your state or Puerto Rico, it will be both federal and state tax
free.