Calaméo provides a way to publish a variety of interactive, multimedia publications for free. (Registration required.) Very easy to use, and it accepts PDFs and most Microsoft Office and OpenOffice formats. Sounds, videos, etc. can be added to the publication. Sharing can be set for public or private.
Here is a quick example of "An Introduction to the Gospel of Mark" I created.
UPDATE: 2008.06.30 - Here is a thorough review of calameo. A question in the comments noted that it didn't seem there was any way to add multimedia. The way to get to it is, after having created your publication, click on "Links" to open the publication in a new screen and then use the icons to add music, videos, etc. If you click on "Edit," you can change the background and set sharing levels.
HT: Stephen's Web