The payout on three- and six-month Treasury bills reached its highest level since late May in today's auction. The effective yield for three-month bills is now 4.31%; for six-month bills, it is 4.78%. That means, for example, that you would only have to pay $9,767.40 today for a bill that would be worth $10,000 in mid-April. Treasury bills are not only supersafe, but all the interest you earn is free from state and local taxes. That boosts their effective after-tax yield for people who live in high-tax localities.