The Planetary Society has some amazing images & animations of Earth [1] taken by planetary spacecraft.
My favourite at the moment has to be the image of Earth from the surface of Mars [2], taken by the Spirit rover in 2004 and the first image taken from the surface of an object beyond the moon.
[2]Shades of the Total Perspective Vortex [3], for those HHGTTG [4] fans out there.
Speaking of which, Paulo Ang [5] has a rather wonderful Flash animation entitled “The Total Perspective Vortex [6]” which makes powerful use of planetary and astronomical imagery alongside music and a liberal smattering of Hitch Hikers quotes.
