Quod Libet is a Gapless GTK+-based audio player written in Python. Its designed around the idea that you know how to organize your music better than we do. It lets you make playlists based on regular expressions (dont worry, regular searches work too). It lets you display and edit any tags you want in the file. And it lets you do this for all the file formats it supports - Ogg Vorbis, FLAC, MP3, Musepack, and MOD.
Quod Libet easily scales to libraries of thousands of songs. It also supports most of the features you expect from a modern media player, like Unicode support, multimedia keys, and tag editing. More Info »
If you're happy with your current audio player and you don't want to switch to Quod Libet, you can use Ex Falso instead. Ex Falso is a program that uses the same tag editing backend as Quod Libet, but isn't connected to an audio player.