Apple's QuickTime Player is designed to play QuickTime audio and video files. For many years, the player has also been licensed to developers for use with QuickTime files in third-party software applications. Apple itself uses the QuickTime Player as the playback engine for its iTunes software.
Audio formats supported: MP3, AAC in an MPEG-4 (or QuickTime) file, AAC encoded with FairPlay (.m4p files from the iTunes Music Store), Apple Lossless.
URL for download: http://www.apple.com/quicktime/download/standalone.html. (Caveat: the default download site for QuickTime Player (http://www.apple.com/quicktime/download) offers the player bundled with iTunes.)