Earth Mosaic 2009 image by Bree Marie !
If you haven't had a chance to check it out, the Earth Mosaic 2009 project on Flickr is collecting some truly outstanding Earth Day images - so many, in fact, their servers got bogged down for a bit. It's basically just a nice way to spend some time clicking through beautiful photos of our planet.
They are still taking submissions, but you have to be a member of the group and because of the demand, they are placing some sizing restrictions on your uploads.
The end game is to take every photo they receive and create a high-quality mosaic, which you can see an unfinished sample of here.