A couple of guys who like astronomy and know some folks over at NASA have an "Astronomy Picture of the Day. It’s not all space stuff, there are some interesting photos of clouds, storms, etc.
Far more interesting than the homepage (in my opinion) is the archive, which in the grand tradition of The Web, lists every picture they’ve ever had in one long column on a white page with the only image being a gif of their logo. But you get to see at a glance everything they have, and it’s VERY cool.
