Ok, we've all done a bunch of top down, horisontal maps, but I have yet to see a vertical map.
Granted, it can't be the most common set up for a map but I've thought about it and have got some really cool ideas. In a fantasy setting you can come up with a whole bunch of stuff!
-A city on a sheer cliff wall
-A dwarven city in a vertical cave system
-A high and flat spaceship
-A tower or skyscraper
-A part of Mechanus (a plane in D&D)
-A vertical dungeon with some really weird gravitational effects
-A bookshelf
Well... I think you see where I'm going with this.