Research Music Player Daemon (MPD):http://mpd.wikia.com/wiki/Music_Player_Daemon_Wiki
Basically you install a server and client (can be on the same machine) on a PC. Most of the clients have web interfaces and there are even apps for iPhone/Android that let you browse the your music, setup playlists, select songs, etc.
I have the MPD service and a client running on my A100 Popcorn Hour media streamer and control it via my Android tablet. It works great and no need to have a TV on to select songs.
On note this is all shareware so it is not for you if you want an out of the box solution. There will be some fiddling involved to get everything to work correctly.
MediaMonkey also has plugins and iPhone/Android apps that let you control it remotely as well.
Even simpler would be to VLC or Teamviewer apps on iPhone/Android/PC with browser to directly control your media PC and just use your favorite media player.