This plugin allows admins to specify additional file types that are allowed for uploading to the blog.
By default, WordPress only allows a very limited set of file types to be uploaded. This set is defined by a so called "white list". What's not on the white list can't be uploaded.
This plugin allows you to extend this white list through a settings page.
Additionally it comes with a wide range of file types that are enabled automatically, like audio files (ac3, mp4, ...) and video files (avi, mkv, ...).