foobar2000 (audio player)
I have grown to love foobar, but I will say it is not for everyone. Foobar2000 is a slimmed down audio player with a minimalistic interface. The lack of feature clutter makes it more powerful to me. But it is missing things that most normal people will want, like library sorting. If you want a more feature rich audio player then I have to recommend MediaMonkey, which I also love.
I use foobar2000 for my FLAC collection and MediaMonkey for my MP3 collection.
Alternate choice: MediaMonkey