Today, August 15th, is the deadline for individuals who filed extensions to actually file their 2004 Federal tax returns. A second extension is available (until October 17th), but you need to have a reason (and have the IRS accept the reason); use Form 2688 to file for the second extension. For Californians, your extension to file is for six months; you need not file your State return until October 17th.
Next year, the automatic Federal extension will be for six months.