Metastream - Watch streaming media with friends
VLC Media Player - VLC is a free and open source cross-platform multimedia player and framework.
Watch2Gether - Watch2Gether is an app that allows multiple people to watch the same content simultaneously and interact with each other while watching.
foobar2000 - An advanced freeware audio player for the Windows platform.
Hyperbeam - A better way to watch together online
Winamp - Winamp is a media player that allows users to play multiple-file formats, arrange media in a varied file-management system, and play unique media with AAC encoding.