Today's Astronomy Picture of the Day does a very good job of illustrating our solar system and gives a good visual reason for the demotion of Pluto. Be warned, though... when it says click on the picture for a bigger version, they're not kidding: the original is 1.3MB, 6000+ x 3500ish pixels. Perfect for teaching aids, if you've got a big color plotter than can handle something like that.