When Muhammad Ali, then still known as Cassius Clay, left Rome in 1960 as the Olympic gold medalist at light heavyweight, he was already a household name in the United States. When Ray Leonard captured gold in Montreal in 1976, it launched him onto the cover of a Wheaties box.
In an earlier, less-sissified media culture, Olympic boxing was a major draw for network coverage. Some of the great pound-for-pound boxing stars of recent decades launched their careers at the Games.
Note that this list is ranked largely on what the fighters went on to do as professionals. In the Cold War era, a number of Eastern European and Cuban fighters could very likely have had successful careers in the pro ranks.