I am filing as the executor of my dad's estate. What do I need to send in with the 1099 besides the letter of testamentary?

[AmyT]

There should be an fiduciary return (Form 1041) prepared for the estate.

Any income and expenses of administering the estate should be reported on the estate's fiduciary return.  Note:  Form 1041 is not required for an estate with less than $600 in income.

Depending on the election made when the estate received it's TIN (taxpayer identification number), the estate may have a year end that is not December 31.  If this is the case, the return will be due 3 months and 15 days after the fiscal year end of the estate.

The fiduciary return can be filed using TurboTax Business (https://turbotax.intuit.com/small-business-taxes/).  If you are not comfortable preparing the return, a CPA or attorney who specializes in estates can assist you.