That damn KQ5 ANT song is still stuck in my head all these years later. I sometimes find myself singing it suddenly, haha. Love it though
That and "Land Beyond Dreams", Erana's Peace, any QFG song really. And I like the main themes from Colonel's Bequest, Police Quest & Eco Quest.
LAND BEYOND DREAMS: http://www.youtube.com/watch?v=71iVo3dW9mY