Free downloadable or online geospatial tools and programs:

Google Earth - Google's global viewer

Google SketchUp - Google's 3D design tool

NASA World Wind - NASA's global imagery viewer (includes virtual globes for the moon and Mars)

ArcExplorer - ESRI's GIS data viewer

ArcReader - An ESRI mapping application for viewing and printing maps and globes

Virtual Earth - Microsoft's "Local Live" tools

Google Maps - Google's mapping and routing tools

Flash Earth - Virtual globe layers rendered in Flash

GloVis - Landsat imagery viewer