The M60, though still in sevice, has largely been replaced by the M240B in the regular army. They both fire 7.62 X 51mm NATO (.308 in). The newer weapon is smaller and lighter though its range capabilities are more medium range than long. The M249, which soldiers refer to as the "SAW" for squad automatic weapon (although squad automatic weapon is really a class comprised of all these weapons), fires the 5.56mm rounds that go through the M16A and M4.
In the regular army the M16A is usually only carried by auxillary personelle these days. Combat units opt for the lighter and more wieldy M4.
And dentists in the army carry a shitty little M9.
I hope in the future Americans are thought of as a warlike, vicious people, because I bet a lot of high schools would pick "Americans" as their mascot. -Jack Handy