With short-term interest rates coming down, it's getting tougher and tougher for income investors to find a decent yield.Where can you go? Here are three ideas. Certificates of deposit: There are still some bargains out there. This weekend, days after Ben Bernanke slashed interest rates to 4.75%, you could still find bank CDs out there yielding 5.5% or better. Picks include an IndyMac Bancorp ( IMB) six-month CD with an annualized yield of 5.7%, a one-year CD from Countrywide Financial ( CFC) yielding 5.65%, and a three-year from MetLife Bank (a unit of insurer MetLife ( MET)) yielding 5.35%. Why haven't they been cut yet in line with other short-term rates? Bankrate.com's Greg McBride says each bank is reluctant to be the first one to cut. And it still makes sense for them to borrow at these levels. "We haven't seen yields pull back too much," he says. "It's still cheaper for banks to pay 5.5% in a CD than it is for them to go raise funds in the credit markets." Money invested in a CD is guaranteed by the Federal government up to $100,000. But grab 'em while you can: Once the rates start falling, you probably won't see levels like this again for quite a while. Municipal bonds: They are as safe as your state and local governments, and right now they are going cheap. Thirty-year munis are yielding around 4.9% right now, or nearly as much as Treasuries -- but in the case of the munis, the income is free of federal income tax.