Since you are almost certain that youu2019ll have to pay 500k next year, you need to be extremely conservative. The FDIC insures up $250,000 in banks and credit unions so splitting it up into a savings and a checking account would guarantee the principle but minuscule return.Another option is a money market account. Check out Everbanku2019s Yield Pledge Money Market and Yield Pledge Checking are offering 1.11% for balances up to $250k (perfect just split the 500k between the 2 accounts and earn an easy $5520!) Hereu2019s a link Earn in the Top 5%.This may be the best return you can get for a risk free one year investment since the higher rates are reserved for those who will be investing their money for a longer duration.