https://help.ubuntu.com/community/RestrictedFormats
Bookmark it - it's a gold mine of info for everything-media within Ubuntu.
Edit: The best way to cover everything is to find your Version on the above-linked page and follow the basic steps for enabling all the Repositories. After that, scroll down to the bottom and select the specific areas (audio, DVD, etc.) via the links. Make sure you add the Mediabuntu Repo's, too - I think the link for it is somewhere on the DVD page.