We had the contest in which the players could create a weapon skin, and the first 3 skins can be obtained in the game now.
I really suggest and I hope this idea will be considered to create a 'Compose A Music Piece' Contest, in which the contestant will have to compose one orchestral music piece, based on a motif from Guild Wars 2- for example Fear not this Night and create something new out of its notes.
If there will be many entries, then first 3 composed music pieces will be added to the game in some form- in a trailer, during the story or as the music box. And maybe some extra rewards sponsored by Arenanet for example to meet Maclaine Diemer and some members of his team.
The Music of this Game is everything to me, gave me so many inspiration, and made me love the Music in general.
Seek, and you shall find.