@matt I use Audacious (currently with the GTK+ 2.x interface because the Qt5 interface hasn't re-implemented global hotkeys and I don't feel like binding a dozen different things through xbindkeys and audtool) because it's the right balance of a UI that I can customize to be minimal and an unbeatable set of bundled format-support plugins.
QMMP is the runner-up I'd choose and it's essentially Audacious's Qt-based competitor from before Audacious supported Qt as a frontend option.