NameChanger is designed for the sole purpose of renaming a list of files. To install just download the disk image, open it and drag the app to your Applications Folder.
Need more options renaming your files? Open the options pallet by clicking the Options button. From here you can hide the file extensions or change the checked and selected files.

The checkbox to the left of each row allows you to choose which files will be renamed. This allows you to pull in a number of files once and rename subsets as you wish, without constantly adding and removing files. If the box is checked, the file will be changed, otherwise the file will go unaltered.

Hiding the extensions is often useful when you need to append something to the end of the filename, but not alter the file extension. Check the ‘Hide Extensions’ checkbox and rename as desired.