The Harris Poll has some new data on the most and least trusted occupations. Respondents were asked, "Would you generally trust each of the following types of people to tell the truth, or not?"
Doctors are at the top with 85% percent generally trusting them. Actors are at the bottom with only 26%. A few other categories:
The President: 48%
Members of Congress: 35%
Additional information, including the results for all 22 occupational categories, can be found here. Unfortunately, the results do not reveal what happens when you combine a professor and a lawyer.