Being president pays; $400,000 a year, in fact.

That salary has increased over time. President Harry Truman left office in 1949 making $100,000. When Richard Nixon entered the White House in 1969 the salary went up to $200,000. It remained there for 30 years, until Congress doubled the presidential salary effective in 2001, when President George W. Bush took office.

Aside from the pay, there's the free transportation in the presidential limousine, Marine One and Air Force One. And don't forget the free housing in Washington's most famous mansion, complete with a killer view of the Washington Monument, along with other perks (a personal chef, for one).

When a president leaves the White House he's still on the government payroll, receiving an annual pension of about $200,000, health care, paid official travel and an office.

Rent for President Jimmy Carter's Atlanta office is $102,000 per year, according to 2010 figures compiled by the Congressional Research Service. President George H. W. Bush's Houston office costs $175,000 per year. President Bill Clinton's office in the pricey real estate market of New York City is $516,000.

Not too bad, huh?

But these taxpayer-funded benefits are nothing compared to the big bucks presidents rake in writing books.

"My Life" netted Bill Clinton a $15 million advance.

George W. Bush earned $7 million for the first 1.5 million copies of "Decision Points."

Jimmy Carter has written 14 books.

"He was broke when he came out of the White House," presidential historian James Thurber said. "If you can write or you can write with someone else, you can write a book and make a great deal of money. Jimmy Carter did that."

President Obama wrote "Dreams From My Father" in his 30s. Initially, it was only a modest success, selling better as his political star rose, flying off shelves when he ran for president.

"I have been blessed," he said on the campaign trail in 2008. "Before this book started selling we were living in a condo and we had two cars, but one of them was beat up."

Book sales are still the Obamas' main source of income.

For the biggest payoff without too much work, speeches are the way to go. And Bill Clinton is the reigning king of the podium.

Right after Clinton left the White House in 2001, the Greater Washington Association of Executives paid him $125,000 for a speech, a very standard price for a former president.

"I've never had any money until I got out of the White House," Clinton told CNN's Wolf Blitzer in 2010. "But I've done reasonably well since then."

That's quite the understatement. Since 2001, he's earned $75.6 million giving speeches to corporations and organizations around the world, according to the latest financial disclosure required of his wife, Secretary of State Hillary Clinton.

The Center for Public Integrity estimates George W. Bush has made $15 million from speeches since leaving office.

All of that money raises questions.

"I think the American people think American politics is all about money," Thurber said. "And this certainly doesn't change their view."

In 1989, right after President Ronald Reagan left the White House, he was lambasted for accepting $2 million for two speeches in Japan, then an economic foe of the United States.

Not all presidents have gotten rich after leaving office.

Harry Truman couldn't afford to answer the copious mail he received or respond to requests for appearances. This prompted Congress to adopt pensions and benefits for former presidents in the 1950s so they weren't forced into activities deemed unsuitable for a former head of state.

Some presidents come into office already very rich. If elected, Republican presidential candidate Mitt Romney would fall into that category. With a net worth of about $200 million, he would be the third-richest president in history.