The Chronicle of Higher Education has data on 2007-2008 salaries for professors at various ranks (Assistant, Associate, Full Professor) in various departments.
Professors teaching Law, Business or Engineer were among the highest paid.”Among new assistant professors, those in business had the highest average salary, at $86,640. The three disciplines with the lowest average salaries for full professors were English, visual and performing arts, and parks, recreation, leisure, and fitness studies, the survey found.”
Salaries also varied by the type of institution. Professors at Doctoral Institutions made the most, followed by Master’s Institutions. Professor teaching at two-year colleges had the lowest salaries.