ARScope is an interesting combination of old world metaphors such as a magnifying glass and a crystal ball, head mounted display and projected AR. The user holds a handheld device covered by reflective material, on which an image is projected from a micro-projector the user wears on his head. Two cameras, one on the handheld device and one on the headset, and a sophisticated algorithm are used to calculate the user's point of view relative to the handheld device, and thus ARScope is able to project a suitable image. In the case of the crystal ball, it even allows two users to see two different perspectives on the augmented world.
Can't understand why no-one has commercialized this idea yet. It seems to be far more natural than HMD that blocks your peripheral vision.
Another video can be found here, and an interview with one of ARScope's creators is here. More details on the project's website.