The QGIS Elevation Plugin is available from http://polylinie.de/elevation
Quantum GIS is available from http://www.qgis.org
Functionality: The plugin will obtain and display point elevation data using the Google Maps API.
Use of the extension requires acceptance of the Google Maps Terms of Service: http://code.google.com/intl/en/apis/maps/terms.html
The installation can be installed by selecting Plugins->Manage and Install Plugins... from the menu followed by a click on "Get more".
Installation from the source tarball is also possible.