First, why is this a human rights issue? Well, there’s article 23 of the Universal Declaration:
Everyone who works has the right to just and favourable remuneration ensuring for himself and his family an existence worthy of human dignity, and supplemented, if necessary, by other means of social protection.
And there’s generally the issue of the absence of poverty as a human right. A minimum wage is obviously intended to protect people from poverty. Economists disagree on the effectiveness of a minimum wage: some believe it helps to combat poverty, others say that it increases poverty because minimum wage level regulation creates job losses: the price of labor will be higher than the price that would be fixed by unhindered supply and demand of labor (read here why this is supposed to be the case). And job losses mean more poverty. However, the evidence for this is mixed, to say the least. See here, here, here or here for studies that show no adverse employment effects of a minimum wage.
In the U.S., when state and federal regulations differ, the higher of the two rates applies. Currently (2009), the “minimum minimum wage” is $7.25 per hour. A minority of states has minimum wages higher than the federal minimum.
An updated version of the map: