Jonathan White, an assistant professor of surgery at the University of Alberta, recorded a few podcasts for his students. "Each podcast is meant to answer basic questions that students may have on a given topic and is designed to be used in conjunction with their class notes and textbooks." He recorded them and forgot about them - until the emails started coming in. The podcasts had gone viral. "His Surgery 101 podcasts now average about 1,000 downloads a day, or roughly one every two minutes, from around the globe." Here's the podcast page.