Many people who visit this site are searching for pictures of earth from space.
Well, obviously there is no better source for that than NASA. Because this is so hugely popular, NASA has made a own site for that under the slightly cryptic name of: http://earth.jsc.nasa.gov/sseop/efs/
Here you can find all sorts of images of our beautiful planet. And what is best, almost all material from NASA is public domain, that means you are allowed to use it for your own purposes as long as you state the source of the pictures.
Another excellent NASA source for pictures of earth and pictures of space exploration in genereal is
There you will find such treasures as this one and a lot more: