Smooth 3D Fly-throughs
I really like seeing the cool stuff people are doing with 3D GIS. It could be improved, however, if fly-through paths were based on laws of aerodynamics. Granted, putting aerodynamics into GIS would be a major undertaking. But what about taking an open-source flightsim package such FlightGear, and use it to generate flight paths that the GIS would then use for generating animations?
Or, maybe add a globecontrol to flightgear so you could be flying through your GIS, controling throttle, flaps, etc.