VLC Media Player - VLC is a free and open source cross-platform multimedia player and framework.
Mixxx - The most powerful free DJ software in the world.
foobar2000 - An advanced freeware audio player for the Windows platform.
VirtualDJ - Virtual DJ Software - MP3 and Video mix software for DJs
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.
Traktor Pro - Flagship DJ software with four decks and a stunning range of creative features for maximum freedom in DJing.