Windows only: Tiny utility Caffeine disables or enables the screensaver by simply double-clicking on the icon in the system tray—so you can watch that YouTube video without your screensaver kicking in.

Windows only: Freeware application WPanorama turns your panoramic photos into videos or screensavers. We've already shown you how to stitch your photos into beautiful panoramas, but once you've done that, there aren't a lot of great ways to show them off. WPanorama animates the image as though you're a viewer standing in the centre and looking around the full 360 degrees. If your panorama doesn't make the full 360-degree trip, it just moves back and forth from one side of the photo to the other. WPanorama is freeware, Windows only. WPanorama

Mac OS X only: Donationware application Status Screen Saver adds status notification badges for popular Mac apps like Mail, NetNewsWire, and Twitteriffic, to the bottom of your monitor while your screensaver is playing. Considering the number of times we shake our mouse to exit screensavers just to see if we've received a new email, Status Screen Saver is a brilliant idea. Your screensaver continues running while you stay abreast of those updates. Status Screen Saver is donationware, Mac OS X only, works with any already-installed screensaver. Status Screen Saver

Mac OS X only: Turn your desktop into a photo slideshow using freeware app Wallsaver. Wallsaver is a very simple application written in AppleScript that replaces your wallpaper with the current screensaver. Setting the wallpaper as Flurry (shown above) is pretty annoying, however, using your pictures folder is an excellent way to use your desktop as a digital picture frame. A few months ago we showed Linux users how to get the same effect using a nautilus hack. Thanks, NineTailedFox!
Wallsaver