The map at the top of this page shows in red which countries formally permit women in combat positions. Shown in orange are countries that allow women to serve in military roles that involve fighting but not front-line combat. That typically means fighter pilots. In South Korea, women also serve in artillery and armored units.
A note on the data: It comes from piecemeal sources, mostly gathered by Foreign Policy's Joshua Keating in this great overview (see also: National Geographic, NPR, New York Times). Rules and their enforcement for military servicewomen vary in different countries. And it's possible that women serve in de facto combat roles in some countries not included here.
The maps shows that the countries where women may serve in military combat roles are mostly European. It's permitted in all Scandinavian countries, which famously have the narrowest gender gaps in the world. It's also prevalent in the Anglosphere, where it's allowed in Canada, Australia and New Zealand, with the United States and the United Kingdom the last hold-outs.
Otherwise, the only other countries that allow women in combat are Israel, Eritrea and North Korea: an odd mix of nations that use conscription to maintain large militaries. In all three, cultural solidarity with the military and history of armed conflict may play the biggest roles in that particular form of gender equality. But I'm not sure what may have led South Africa and Pakistan to break from their regional norms and permit women to fly combat aircraft.
Here's a list of the countries that allow women in front-line combat positions. In Europe: Denmark, Estonia, Finland, France, Germany, Lithuania, Netherlands, Norway, Poland, Romania and Sweden. Elsewhere: Australia, Canada and New Zealand in the Anglosphere; plus Eritrea, Israel, and North Korea.
And here are the countries that allow women in positions such as fighter pilots. Pakistan, Serbia, South Africa, South Korea, the United Kingdom and the United States, at least until Panetta's change takes effect.
Formally, American servicewomen who want to serve in combat may do so only in support roles, although a number of those women do end up seeing combat. Women may also hold serious but non-frontline jobs, such as flying fighter jets or staffing ballistic submarines.
In comparative, international terms, the U.S. move to allow women in combat roles is not unusual. If anything, it will make the United Kingdom's policy of keeping women off the front lines even more of an outlier than it already is.