A Window to the Past, is a sad-ish and still comforting sad music. My new found favourite. From Prisoner of Azkaban
Hogwart's Hymn, its the most moving orchestra piece ever. From Goblet of Fire.
Black Lake, very spooky, helps me when I am trying to imagine dark underwater scenes. From Goblet of Fire.
Fawkes the Pheonix, just reminds you of Hogwarts. From Chamber of Secrets.
Harry in Winter, winter scenes, cold and comforting.
Opening, my favourite starting tune from Half Blood Prince
Wizard Wheezes, jazz!
Farewell Aragog, another favourite from Half Blood Prince, where Professor Slughorn says a speech of farewell to dead Aragog.
When Ginny kissed Harry, this one is a bit different, I think they used harp or guitar. It does sound like a good memory.
The Friends, from Order of the Phoenix, this is warm and melancholic too, but beautiful.
I don't listen to them everyday, because it will become too common place if I do. I listen sparingly.