With 8.848m height compared with the sea level, Everest is known as the world's highest mountain but this is not the highest compared with the center of the earth. Although lower than the Everest 2.500m but mount Chimborazo in Ecuador is the highest point from the center of the Earth.
The reason of this different is because the earth is not round, the globe is a sphere flattened at both side so our planet should be wider at the equator. Chimborazo point one degree different to the equator due to it should have a height of 6384 km from the earth center (2 km higher than Mount Everest).
Information : http://www.npr.org/templates/story/story.php?storyId=9428163
Image : http://genesys33.files.wordpress.com/2008/05/chimborazo.jpg