During a muzzleloader hunt in Colorado, we were on a ridge across from at least 20 mature 6-point bull elk. They were scattered around across the canyon less than 400 yards away. There was hardly a 5 second break without a bugle. This went on for hours and I probably heard 1000 bugles in that one spot. I remember wishing I could share it with everyone. It was an incredible experience.
I've also heard lions roar. The first time, outside of a zoo, was my very first evening in Africa, in Namibia, near the Botswana border. When they are close, it's a sound that communicates directly with your primeval brainstem. It provokes an emotional response. Hearing the sounds that come out of a lion that has just been shot is also something that will stay with you.