If you installed
Google's photo screensaver but you can't find MediaRSS feeds to add,
Framechannel lets you create a feed from more than 200 channels of photos that include NASA's photo of the day, travel pictures, images from National Geographic, news and weather. You have to create an account, select your favorite content and copy the URL of your feed. Then add the feed to Google's screensaver. The cool thing is that the URL of the feed remains the same even if you add or remove a channel.
For those who don't want to install Google Screensaver, there are
alternative programs or plug-ins for Windows and Mac.
