FastStone Image Viewer is an image viewer and editor that deserves to be singled out - not only because it is free, but also because it offers a strong combination of speed, usability and versatility.
Viewing
While the viewing functionality is a no-brainer, FastStone Image Viewer comes with a range of methods with which to browse pics. First off, there is the standard file browser that displays thumbnails of your images with a preview window for the file that is currently selected. FastStone Image Viewer also offers an option to check out individual pictures in full-screen. When you're in fullscreen, remember, you'll also have access to the full range of FastStone Image Viewer tools.
Editing
However, FastStone Image Viewer goes beyond simply displaying images. You can perform quick edits to really bring out the best in your pics, such as adding a stylish frame that acts as a mask to reduce the sharp edges or, if you happen to be working with 3D, FastStone Image Viewer also offers a very effective bump map option that will serve you well for texturing. There are of course the standard tools of brightness/darkness adjustment, sharpness/blur, grayscale, red-eye removal and more.
Batch tools
Further great features come in the form of batch rename and convert options. These could prove invaluable to many web developers looking for a quick way to prepare their PSD files for the web. With the inclusion of these batch functions, it would have been good has FastStone Image Viewer pushed the boat out even further with an option to apply batch effects, for example to brighten up a group of photos that were taken in a dark space but alas, it's not there!
Looking for faults with FastStone Image Viewer is like looking for the corner of a circle, although if you insist on nitpicking, you can say that in the thumbnail browser view dragging and dropping should be possible for moving files. However when you realize that it is possible to drag and drop with the left nav bar that argument looses its legs.
There's healthy competition in the image viewer arena, but thanks to the innovative features of FastStone Image Viewer the bar has been raised to new heights.
