Automation apps can help you quickly rename multiple files or folders. They have several ways to rename files. You can find and replace characters in a filename, add extensions, number files sequentially, etc.
End the monotony!!!
Update—Newer Apps:
Since the R-Name app is becoming a bit outdated, here are two alternatives that work well—and they’re free!
NameChanger
With NameChanger, you can rename a list of files quickly and easily—and see how the names will change as you type. It’s designed for the sole purpose of renaming a list of files. To install just download the zip, open it and drag the app to your Applications Folder.
Rename
Rename is a straightforward freeware application that allows you to rename files with ease. Its additional features for searching files makes it a good program for many users.