This is a site I like to visit every day (and if you miss a day, you can always page backwards to preivous days through the links at the bottom of the page). Today's picture is a great one. If you click on the picture, you will be taken to a larger resolution of it. I keep a collection of these for screensavers and wallpapers.
The general Pic O The Day is at http://antwrp.gsfc.nasa.gov/apod/astropix.html
The larger version of today's picture is