In about ten minutes or less, you can file your extension online. If you are sending payment, you'll be able to set up a direct debit from your checking account.
You can also send payment (and get an extension) by credit card using Pay1040 or Official Payments. Both companies charge a 2.49% service charge. Because of this service charge, it may be cheaper just to pay the IRS in a month or two. That's because, with an extension, the IRS will charge you a penalty of half a percent per month for late payment plus interest of 5% annual. This works out to be equivalent to a monthly financing rate of about 0.92%. So if you will be able to pay within two months, you'll save some money by just getting an extension, and then sending in payment later.
You can also file your tax returns online using top-rated software from CompleteTax, TaxACT, TaxCut, and TurboTax. The caution here is we often make mistakes in data entry or overlook valuable deduction in the rush to meet the filing deadline. You'll often come up with better numbers by working on your return calmly after the 15th.