The Astronomy Picture of the Day archive has some fantastic pictures. I used to check them on line when I had time but I recently moved to the APOD wallpaper program. It is a neat program that automatically updates the desktop with the latest APOD picture and explanation. Starting the day with a beauty like The Cat's Paw Nebula is a pleasure:
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Astronomy Picture of the Day is a web site hosted by NASA and maintained by professional astronomers who pick a new exciting beautiful astronomy picture every day. Astronomy Picture of the Day has been active for more than 7 years, successfully sharing the beauty of the universe with us all. APOD brings it one step further, setting those beautiful astronomy pictures, optionally with their scientific explanation, as your desktop wallpaper