How far a sound carried depends on the volume of the sound, which is measured as the pressure of the sound wave, and the density of the air or other medium the sound flows through. Thinking of sounds traveling in air, the volcano, Mt. Tambora, erupting in 1815, was heard 1,600 miles away. (That means, if the volcano had been in Boston, MA, it would have been heard all the way to Houston, TX.) The largest volcano ever known to erupt in geologic time was about 50 times larger. It might well have been heard 12,000 miles, which is to say, all the way around the World. (http://en.wikipedia.org/wiki/List_of_largest_volca...
If you count sounds traveling through the Earth and detected by machines, seismographs detect earthquakes on the other side of the world, because sound travels farther through the dense earth than through thinner air.
Since sound can't travel through outer space, a sound traveling around the world is about as far as it can go.
On to more normal sounds. I think loud thunder can be heard five miles away. A plan breaking the sound barrier can be heard several miles away, too.