Foobar2000 is an advanced audio player for the Windows platform. Some of the basic features include ReplayGain support, low memory footprint and native support for several popular audio formats.

foobar2000 Features
Audio formats supported: MP1, MP2, MP3, MP4, MPC, AAC, Ogg Vorbis, FLAC / Ogg FLAC, WavPack, WAV, AIFF, AU, SND, CDDA.
Full unicode support.
Advanced tagging capabilities.
Support for transcoding all supported audio formats using the Converter component (requires external commandline encoder executables for different output formats).
ReplayGain support - both playback and calculation.
Customizable keyboard shortcuts.
Open component architecture allowing third-party developers to extend functionality of the player