Google Earth has a Photorealistic 3D Buildings layer that
If you're thinking this sounds good, but difficult and/or expensive, don't fret. There are lots of free tools to get you started. Google SketchUp is an easy-to-use 3D modeling program that you can use to construct the architectural models and apply photographs to them to generate photorealistic buildings. It's free to download, and there are lots of tutorials available to help you learn the program, and specifically to help you construct a model that's optimized for Google Earth. You can then upload your model to the 3D Warehouse, add descriptive information, and mark it for inclusion in the "Photorealistic" 3D Buildings layer in Google Earth. Alternately, your city GIS department may already have models of your downtown that you can start with; or you may want to use some other software package to build your models. If you'd prefer not to upload your models using Google's 3D Warehouse, you can contact the team behind the Cities in 3D program to learn about another way to add your models to Google Earth.