The Dynamap seems to be a good example of dense informational design. They managed to present a standard map (the paper kind) with three different maps on it, a street map, a subway map and a landmark map.
By rotating the map, you get the three maps. Much like those old Cracker Jack Stickers (rotate it and it moves!). By using technology (one word: plastics), they seem to have it nailed where it's a smooth transition, and easy to switch between these maps.
I'd like to get my hands on one, see what's going on.