Last weekend I discovered (1) that Google Earth was even more amazing than I had previously thought [and now they have a Mac version as well!]; and (2) there is a lot more out there in terms of digital geography if you look a bit harder.
Here is for example this USGS site from which you can download (with some patience) not only the usual satellite imagery but digital elevation models (DEMs) as well, for pretty much the whole globe [thanks to my friend Radu Girabcea for pointing me to it]. Once you've got a DEM, you can use 3dem, a nice little piece of freeware to display the elevation models in 2D and 3D and to drape georeferenced images over the topography. DEMs are available (for free -- at least at this point) with a ~10 m resolution for most of the US and a ~30 m resolution for other areas (I was especially excited to savor the detailed topography of the Carpathians -- the more familiar you are with a place, the more illuminating it can be if you examine the morphology).
Another thing worth taking a look at is NASA's version of Google Earth, that is, World Wind. With one click, you can switch from Landsat images to USGS topographic maps [although I often have problems with the server connection]. Can it get a lot better than this?