From the Secret Service website
* The president, the vice president, (or other individuals next in order of succession to the Office of the President), the president-elect and vice president-elect
* The immediate families of the above individuals
* Former presidents and their spouses for their lifetimes, except when the spouse remarries. In 1997, Congressional legislation became effective limiting Secret Service protection to former presidents for a period of not more than 10 years from the date the former president leaves office
* Children of former presidents until age 16
* Visiting heads of foreign states or governments and their spouses traveling with them, other distinguished foreign visitors to the United States, and official representatives of the United States performing special missions abroad
* Major presidential and vice presidential candidates, and their spouses within 120 days of a general presidential election
* Other individuals as designated per Executive Order of the President
* National Special Security Events, when designated as such by the Secretary of the Department of Homeland Security
http://www.secretservice.gov/protection.shtml
Thanks, porter_knorr!
That should resolve all questions!