Mac OS X only: Free utility File List batch renames files on your Mac according to criteria you set up. Rename files using sequential numbers, prefixes or suffixes, or change to upper or lower case. File List supports advanced file naming specs that let you use conditional statements, too, like "if it's a .TIFF file rename it to PHOTO." Best of all File List can create file renaming "droplets" that you can pin to Finder's toolbar for drag and drop easy reuse. File List is a free download for Mac OS X only.