Use Form 4868 to obtain the automatic six-month extension of the time to file your tax return. Note that this is not an extension of the time to pay your taxes, just of the filing due date for your return. If you owe tax and don't pay it by April 18, 2011, interest and penalties will accrue on the balance.
To print this form, click the "Print..." button while the form is displayed on your screen, or select the form from the Print dialog. The form doesn't print as part of your return; it's filed separately with the IRS.