If you're looking for a fast, reliable, and free way to convert many images at once, look no further than FastStone Photo Resizer. From the same folks who publish the excellent Image Viewer, Photo Resizer outputs files in the most popular formats, including TIFF, GIF, JPEG, and BMP. Besides its batch-conversion skills, the application also can rename pictures in bulk. This program lacks any sort of fancy image effects, but you can make basic tweaks, including cropping, rotating, resizing, and adjusting certain aspects of an image's color. You'll even find a tool for stamping shots with a watermark.
This utility demonstrated speedy performance in all tests, and it's not hard to appreciate that its main window can be gussied up with several skins. You can't go wrong with form and function working together, and that's definitely the case here.