Music in MapleStory Classic World is a loop per map: a theme for each town, each hunting ground and each dungeon, that plays as long as you stand there. The wiki hosts the audio, so every track can be played here without the game running, and each map page carries the same player in its infobox for whatever plays there.
Every track
All of them, sortable on any column. The Maps column counts how many maps play a track, so the ones you will hear most sit at the top when you sort by it.
Full alphabetical browser
For a plain A to Z of every track, see Category:Music tracks, which the {{Infobox track}} template fills automatically.