http://directpay.irs.gov/directpay/inactivityPage?lang=en_US
Instructions: select "extension" as the reason; down pay AT LEAST $1 towards your taxes to the US treasury with a direct ACH authorization from your bank account. No need to involve any third party corporation (probably forfeiting your privacy in the process), nor fill out form 4868 and be forced to make an attestation to the government that you have done a good job of estimating of your taxes due.
If you carefully read the full instructions on the 4868 (http://www.irs.gov/forms-pubs/about-form-486 you may notice that in using that form you are authorizing the IRS to -- at its sole discretion, and at any time, for any reason -- VOID your six month extension. If they were to do that, you would be liable for late filing! Now that is a hell of a contract to force you to agree to! This path to getting an extension doesn't force you to attest to anything of the sort. And, unlike the alternatives, such as using a 3rd party or mailing the form (and probably paying for proof of mailing), you get a credit against your taxes.
And, yes, you still have the freedom to file your taxes by April 15, if you wish; you just don't have that monkey on your back. (I presume you are paid up on what you will eventually owe).
Don't say I never gave you anything! It took me an hour and a half, yesterday, to figure this out. The internet search engines place a priority on manipulating you to bend over to corporations.
P.S. Your odds of an audit go down if you get an extension and file later in the year. The IRS reportedly has a quota system. They have lots of agents but as those agents get assigned taxpayers to investigate the number of free agents, and resources available to mount a fishing expedition involving you, goes down. That is just how the system works.