Remember that an extension of time to file your return does NOT grant you any extension of time to pay your taxes. So the sooner you make payment, the better.
Thanks for the responses. So I went to the IRS website. It appears there is a form associated with making a one-time payment. It seems nothing is simple with the government.
That would be about right.
If you will be making payments on a somewhat regular basis, I would recommend enrolling in EFTPS.