You can bank these 6% to 8% dividend yields and sleep well at night.Dividends are a great investment strategy for retirees or anyone else looking for passive income that can pay their bills.But be careful: Chasing sky-high dividend yields is one of the classic mistakes investors often make. Higher yields mean more income for your money, but really high yields are usually a warning sign of trouble within a company. Remember, a dividend is only good if the company can pay it.Fortunately, some excellent ultra- ...