I just finished listening to this series of audio CDs on the great explorers, starting (more or less) with Columbus and going through Cook. It was my first lecture by Portable Professor (as opposed to The Teaching Company) and I enjoyed it. (Only real frustration was that I had downloaded it to the iPod which was then supposed to run through the car's audio system, and the former was often mislabeled and the latter only worked right about a third of the time, so it was annoying trying to get the thing to actually play what it needed to when I wanted it to. Would have been easier to just load the discs one by one).
The series was good and I learned a lot about medieval nautical exploration, and who did what when (something I didn't know before). Interesting side stories that he doesn't go into in great detail were the difficulties calculating longitude (I think Dava Sobel's book Longitude is a must-read here) and the search for the Northwest Passage, which I suspect there's a lot of interesting stories about.