Ellen Johnson-Sirleaf, President of Liberia.
Wikipedia has a list of women elected to be heads of state (the list does NOT include monarchs or prime ministers)
Countries that have female presidents right now:
Switzerland
Ireland
Liberia
Phillipines
Chile
Finland
India
I think India is a bit of a special case given that (as I understand it) there’s a strong tradition of elected officials from family dynasties. I don’t know if this is true for other countries, as well.
Technically, neither of them were heads of state, but heads of government, as both India and Pakistan also have presidents. Normally both countries’ Prime Minister is the one really in power and the President a figurehead, though in Pakistan military coups sometimes make the president the one really in charge, like right now. India’s current president Pratibha Patil is female, but besides not having actual powers, the President of India is not elected via popular vote either.
Since both Indira Gandhi and Benazir Bhutto held the most powerful positions of their respective countries, they are of course relevant to this thread. I think one can say with confidence that each one ruled with majority popular support, and that the success of their parties was largely to their credit. Family dynasty factor is strong here, since both were daughters of former Prime Ministers. In both countries the dynasty continues: in India the party leader is again female, Sonia Gandhi, and if things had went a little different, she would probably have already become Prime Minister.
Regarding to Beadalin’s list, it should be noted that, as opposed to the PM, the President of India, at least the current one, does not come from family dynasty tradition. Understandably so, as Presidents don’t have that much real power. On the other hand, for example the both female presidents of Philippines (where, like in most American countries, presidents are both heads of state and government, holding the most power) can be seen as following a family career: Corazon Aquino rose to presidency after the assassination of her opposition leader husband made her the central figure of the anti-Marcos opposition, and the current president is a daughter of a former president. Family dynasties are common in many countries, though the leaders are usually male and only rarely female.
We can also say, that the current US presidential succession is already a typical family dynasty with two Bushes in power. And certainly Hillary Clinton becoming president would resemble the Argentinian from-husband-to-wife presidential transfer last year.
There’s also the case of the fourth-largest country, and the largest Muslim country, in the world by population: Indonesia, where the previous president was Megawati Sukarnoputri. Her last name is based on the fact that her father was Sukarno, the first president of Indonesia.
That’s because there are always 2 Captains-Regent at a time and they only serve for six months. San Marino’s government is quite unlike any other nation.
While Isabel Peron was the first woman President she was not the world’s first elected republican head of state. That distinction goes to Khertek Anchimaa-Toka, Chairwoman of the Little Khural of the Tuvian People’s Republic (recognized only by the USSR and Mongolia) in 1940. Then there’s Sükhbaataryn Yanjmaa, acting Chairwoman of the Presidium of the State Great Khural of Mongolia in 1953.
Benezir Bhutto (BB) needs to be clarified. In her first term (1988-1990) she was essentially powerless, she was the head of a minority government, the Senate and Presidency were controlled by opposition parties and the President used his reserve powers very proactively, he appointed officials, made it clear to the Parliament which bills he would veto and by threatening to refuse assent to money bills which would cause the government to fall due to a lack of finances, he ensured that he could push his own legislative agenda through. In her second term 1993-1997, the President was from her own party, and for 2 years she was clearly in control. In 1995 as a result of a huge recession and the loss of the Senate the President became more powerful and he gave her the marching orders a couple years later.