The heart of my maps page is Google's amazing maps API. The create page is basically a Google map control with some javascript that allows one to define a path. I've hacked together the code to export the resulting data as a KML file. This is the "Keyhole Markup Language" that Google uses in their Google earth program.
Now that I've defined a route and saved the resulting KML file, I use the US Geological Survey's nice, publicly accessible web services to get the elevation. Detailed documentation of the services I use is located here.
Now that I have all the elevation data, I use ImageMagick to create the profile and route preview images. This is a fantastic set of free tools for image manipulation that can be used manually from the command line or automated with many programming languages. I control ImageMagick via Perl with the PerlMagick interface.