Foobar 2000 - very usable player

Foobar2000 is an advanced audio player for the Windows platform. Some of the basic features include full unicode support, ReplayGain support and native support for several popular audio formats.
Features
* Audio formats supported: MP1, MP2, MP3, MP4, MPC, AAC, Ogg Vorbis, FLAC / Ogg FLAC, WavPack, WAV, AIFF, AU, SND, CDDA, WMA.
* Full unicode support.
* Advanced tagging capabilities.
* Support for transcoding all supported audio formats using the Converter component
* ReplayGain support - both playback and calculation.
* Customizable keyboard shortcuts.
* Open component architecture allowing third-party developers to extend functionality of the player.
* Multiply playlists

http://www.foobar2000.org/