According to Payscale, the majority of postdoctoral researchers in the United States earn between $36,408 and $47,858 per year (as of 2010). The pay may go up or down according to the relative prestige afforded the position and based on the researcher's experience and qualifications. When accounting for bonus pay, the average salaries increase to between $36,454 and $48,257.
Science post-docs earn more than post-docs in the humanities or social sciences, though all U.S. fields fit roughly within the overall range. Differences in pay are slightly noticeable between the Ivy League schools and other large research universities. That is, Ivy League institutions manage to pay postdoctoral researchers somewhat better than state schools or other non-Ivy private schools.
Government post-docs pay far better than post-docs in any university setting. For example, you can expect to earn between $42,550 and $54,045 in a post-doc with the National Institutes of Health. At the Argonne National Laboratory, you can expect to earn between $51,016 and $78,611. Argonne, then, pays between $15,000 and $20,000 more to postdoctoral researchers than the average research institution.