foobar2000
Advanced audio player for Windows with highly customisable user interface.
Songbird
A popular music player based on Mozilla’s code. Includes some really useful plugins.
Audacity
Very popular open source software for recording and editing audio tracks and sounds.
iTunes
Music player and video library organiser. Hosts the iTunes Store.
MediaMonkey
Full-featured music player and music collection organiser.
Winamp
Well-known, lightweight, small-footprint media player.
CopyTrans Manager
Alternative iPod manager app. Sync and transfer music & files to iPod, iPhone, iPad.
TagScanner
A multifunction program for organizing and managing your music collection.
MusicBee
A basic music player with a few thoughtful additions, including tag completion.
Tomahawk
A social music player that can pull content from a range of sources including YouTube and Soundcloud.
Spotify
Streaming music service client complete with Facebook integration and iDevice management.
AIMP
Another full-featured audio player expandable with skins and plugins.