The IRS now offers a free and efficient way to make your tax payments online: IRS Direct Pay. Here is the description from their website:
Use this secure service to pay your individual tax bill or estimated tax payment directly from your checking or savings account at no cost to you. You’ll receive instant confirmation that your payment has been submitted. Bank account information is not retained in IRS systems after payments are made.
If you have already made a payment through Direct Pay, you can use the Look Up a Payment feature to view your payment details and status. You can modify or cancel your payment there until two business days before your payment date.
Click here for more information.