Earlier this year I outlined a way to overlay topographic maps in Google Earth, and subsequently get out path information to make maps and upload to your GPS device. The main downside with this method was that Google Earth did not provide elevation data when you created a path, so you would also have to use something like GPS Visualizer to get that information.
I was tipped off by Modern Hiker that the new version of Google Earth (5.2) is out and now it provides the elevation from its digital elevation model (DEM). Now when you create a path, you can right click on it's name in the sidebar and go to "Show Elevation Profile." Something like below should open up:
If you try to save the .kml file, the elevation data won't be included, so use of the elevation is inclusive only to viewing in Google Earth. Still, this addition combined with the topo overlay offers excellent options for route planning.