For Windows VLC is best, for Unix MPlayer is best. These don't offer any library management but that's nothing I need or care about. Of course iTunes does but I think iTunes (and thus Quicktime) is almost as bad as WiMP. For example both can and are abused to popup websites when you try to play the "wrong" files (read: spam). Further both WiMP and iTunes support DRM. This is unacceptable.