Google Earth’s Photorealistic 3D Buildings layer let you host 3D models of the buildings in your downtown annotated with a wide variety of information that people might find useful. Because it's a full, navigable 3D environment, you can go on a virtual tour and get a much better feel for the city than you might from a traditional map. You can click on a building to pull up an information bubble that might contain anything from descriptions of the stores in the building to photographs of the merchandise to a description of the building itself, its construction date, and architect.
With the new Google Earth Browser Plugin you can even place tours of your 3D models on your city's website where people explore them without needing a Google Earth client. Your city could be on the leading edge of the virtual tourism market!
You can use Google SketchUp, an easy-to-use 3D modeling program to construct the architectural models and apply photographs to them to generate photorealistic buildings. There’re 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, explains Google LatLong Blog.