I've seen a ton of moose calling videos, but the one that I'm most impressed with by FAR, is "Love thunder and bull 2". It was made by Wayne Kubat, an Alaskan big game guide. They filmed it down in Koyukuk.
He also sell the bull magnet. A fiberglass cone, made to carry your voice out, but it better serves as a scrape sound on sapplings and brush. I've seen it work firsthand with more than one bull come to us last year.