Quod Libet is a GTK+-based audio player written in Python. It's designed around the idea that you know better than we do how to organize your music. It lets you make playlists based on regular expressions (don't 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.