VLC Media Player - VLC is a free and open source cross-platform multimedia player and framework.
Skip Tunes - Control iTunes, Spotify, or Rdio from your Mac's menubar
foobar2000 - An advanced freeware audio player for the Windows platform.
SpotiMy - Play/Pause and Next/Previous functions for Spotify directly on your Menu Bar!
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.
Bowtie - Bowtie is a desktop accessory that allows you to see and control your music (iTunes, Spotify...