A queue system, in which a user can option+click a song, and it will be placed
  in a queue, whcih will pick the next song.
Stream support for shoutcast/oggcast, or just opening via URL.
Audioscrobbler.
Improved tag reading.
mpeg4 support (FAAD)
look into realplayer (cook in mplayer) and wma
find better ape decoder
visualizer? (libvisualizer perhaps?)
hotkeys for next/prev/stop/shuffle/repeat & info window