Australia's situation in this regard is pretty strange. We have, in fact, a Governor for each state and a Governor General. All are supposedly appointed by the Queen but in reality they are suggested by the Federal or State governments and the Queen rubber stamps them.
The Governor General is the Queen's viceroy in Australia. As such he or she is the actual head of state in Australia. As such he appoints ambassadors, ministers, and judges, gives Royal Assent to legislation, issues writs for elections, and bestows honours. The GG is also the President of the Federal Executive Council and Commander in Chief of the Australian Defence Force.
There was what is referred to as a consitutional crisis in 1975 when the Whitlam government was unable to pass legislation through parliament and thus could not govern the country. The GG at the time dissolved the government and called a general election. The Prime Minister thought the GG was exceeding his authority, but he was in fact just doing his job according to the constitution.
According to our constitution the GG can appoint a cabinet and run the country for six weeks. At the end of that time he must dissolve that cabinet. While this is an emergency power there is nothing to stop the GG from appointing a new cabinet for another six weeks. In fact the office of Prime Minister was not mentioned in the constitution until very recently, even though the Prime Minister had been running the government for 100 years.
Currently he GG is The Honorable Major General Michael Jeffery AC, CVO, MC. He will be replaced in September by our first female GG, Her Excellency Ms Quentin Bryce.
It is likely that General Jeffery will be knighted after his time in office (most are).
Quentin Bryce is referred to as Her Excellency because she is currently Governor of Queensland.