NCsoft maker of many MMO games has started a new company called DirectSong which is a company formed to make music expansion packs for Guild Wars.
Initially I though this was an idea that wouldn't take, but the people creating the music have worked on games like Star Wars Knights of the Old Republic, Harry Potter, Elder Scrolls Morrowind and Total Annihilation. So the music is very good and they are currently selling the whole Guild Wars 23 track soundtrack for just $5.99, so that indicates that the expansion pack should be fairly cheap too.