A few weeks ago, ESRI officially unveiled ArcGIS Explorer (AGE), a world data viewer in the ilk of Google Earth. Rather than try to contrast and compare, you can view this brief MPEG demo. Downloading a version of AGE is free (registration required). You’ll need to download a few "globes" as well to add the data you want to view from the ERSI website that supports AGE. Even more data and resources are available for the also newly unveiled ArcGIS Online, now in a beta mode.