Here are various web tools to visualize the Solar System. Solar System Scope is a beautiful and interactive 3D model of the Solar System and the night sky by Sunaeon. Solar System Visualizer by Michael VanDaniker and Andrew Lund shows the motion of the planets including some extrasolar systems. AstroTour by Gunn Interactive has a very educational demonstration of the orbits of the planets. Also check the NASA/JPL Solar System Simulator and the impressive NASA Eyes on the Solar System for web visualizations that include spacecrafts.