The simpler the access, the more likely people are going to listen or watch. This is Slideshare, which you can now link to an mp3 file to add sound. For music, Slideshare can spread the sound evenly over all the slides. This is extremely easy to do. And free.
SlideShare.net is website where people can upload their Powerpoint presentations (also works with Open Office and PDF files) to share with the world. This is sort of Youtube for slide presentations. There are gems of information that can be useful for teaching purposes. For those interested in emerging elearning, for example, there are a bunch of presentations about Second Life, several of which focus exclusively on it use in education.