There is a lot of these things. Here is another good web page to add to your morning time wasting ritual of reading email and checking your favorite sites for new and interesting stuff.
This is NASA's Earth Observatory site. There is a little of everything here that involves looking down from orbit at the Earth. Most images are in super high-res too and a pretty hefty download in most cases. Here is what Washington looked like last week when we had all the fog, cold and gray weather.
It does have an RSS feed, so you can quickly know when the new images come out.