I'll echo what's already been stated here: I've been looking for a simple, direct, easy - but powerful - file renamer for quite some time. NameChanger fits the bill perfectly.

Bonus: Unlike several other similar utilities, it accepts drag-n-drop. So, I add it to my Finder window toolbar, and can easily rename one (or several) items without even having to think to launch the app first. This is how it should be: It Just Works™.

Perfect implementation. Major kudos to the developer for not only recognizing the concept of Occam's Razor, but for implementing it in his software products.