IHE has an overview; unsurprisingly, the news is not good, and the private-public gap continues to grow. Note the strong average salaries among public universities offered by Rutgers, which has a unionized faculty. Among the private universities, the high average salaries at Princeton are especially notable, given the absence of law, business, and medical schools there, unlike most other schools on that list.
UPDATE: Aldo Antonelli (UC Davis) calls to my attention this (subscription-only) CHE piece on the new AAUP data which notes:
Tight finances on many campuses have led to another year in which average salaries barely increased, exacerbating inequities facing seasoned faculty members, whose salaries are stagnating while their newly hired peers are compensated at competitive market rates.
That anomaly in pay, called salary compression, means that the paychecks of experienced faculty are only slightly bigger than those of new professors. Some fields, including economics and philosophy, are experiencing salary inversion, in which new assistant professors earned more than the average for assistant professors in 2009-10, according to data from the American Association of University Professors. In business administration and management, the salaries of new assistant professors have raised the pay for that rank so much that the average assistant professor earned more than the average higher-ranked associate professor last year.
Any thoughts on what explains this?