See this page. A professor at the NCSU Dept. of Communication is recording his lectures as mp3 and selling them online. He says this is an extra service for (1) students who want to improve the lecture notes they have taken, (2) international students who might have difficulties understanding English, and (3) those who do not want to come to lectures. Since this involves extra recording work for him, he thinks he should get paid.
I suppose there are two issues here. First, the legal issue is who actually owns the right to record the lectures. Is it him, or is it the university, or is it in the public domain? Second, what is the moral issue? Should he be charging the students when they have already paid the tuition fees? How much should he get from the proceeds if the market exists largely because he is already employed by the university?