This is nearly identical to the Automator action "Rename Finder Items." However, for those of you who don't want to sit through creating an Automator workflow, then this might be the application for you! In my opinion, one of the coolest features of this application is being able to create a "droplet." These droplets allow you to simply set up the action you want, create the droplet, then just drag your files and drop them on it to run the action on the files.
This very creative piece of software also won a 3.5/5 from MacWorld's Mac Gems review. This software is available for free (donations accepted) from the Many Tricks website.