Once again via Ogle Earth, a nifty little tool called Elevation Mapper. Enter two positions in Google Maps, either by typing them in or clicking on the map, and get an elevation profile between the two:
Counterintuitively, the “flat Earth” box needs to be checked for this to work.
If you have a DEM (digital elevation model) for an area, you can create a similar profile using 3DEM, either for a straight line or an arbitrary line/GPS track. With a high-resolution DEM, this would give you a more accurate profile.