Sketchup is so much fun, and it's free from google right now. You can very easily make 3D models, texture them, and add shadows. You can put them on google earth, or share them with people using 3D warehouse. The tutorials are easy and fun, easy enough for kids. My son has been making some amazing stuff. Here is what I made this morning, it's a model of our living/dining area, so that I can play around with furniture arrangement.