Some pretty cool satellite images of earth. I particularly like the Ancient Observatories section.
Need some perspective? Take a look at how small we are...
Feeling a bit destructive? Or just want to see if you can knock the earth off of it's rotation? (If you do, let me know!) Try playing around with the Earth Impacts Effects Program. It's "an easy-to-use, interactive web site for estimating the regional environmental consequences of an impact on Earth. This program will estimate the ejecta distribution, ground shaking, atmospheric blast wave, and thermal effects of an impact as well as the size of the crater produced." It's all text based, but so fun!
The photo gallery from the Chandra X-ray Observatory. Lots of really cool pictures of space.
And they finally feel like they have a pretty good idea what causes the Aurora Borealis.