If you're looking for a program to simply play your music, then I would suggest VLC. It will play any/all formats of video/audio. It also has options for the most advanced of users.
If you're looking for software to manage, edit and organize your entire collection... The answer is simple. MediaMonkey is, from my experience, by far the best option. Here is a short description from their site:
Manage a movie / music library from 100 to 100,000+ audio/video files and playlists; whether Rock, Classical, Audiobooks, or Podcasts; Movies, Home videos, or TV shows; whether they’re located on your hard drive, CDs, or a network. Organize, browse, or search music by Genre, Artist, Year, Rating, etc., and never waste your time trying to find the files you know you have.
MediaMonkey is the movie and music organizer for the serious collector.
* Supports MP3, AAC (M4A), OGG, WMA, FLAC, MPC, WAV, CDA, AVI, MP4, OGV, MPEG, WMV, M3U, PLS, etc.