Duplicate Cleaner is a free utility that scours your hard drive for duplicate files. Why? To save you some hard drive space, obviously. But I have a much better reason to use this program.
Duplicate Cleaner is great for identifying duplicate media files -- like music and video. That's awesome, because those suckers take up a lot of space. But have you ever started working on a document in your My Documents folder, and then saved a copy on the desktop for easy access? Heck, maybe a copy ended up out on a network share and some "Drafts" folder on your external drive. Oh, and the USB key, too. Which one is the latest version? How many copies are there? Duplicate Cleaner helps you find all the various incarnations of your documents and whittle them down to just the one you want to keep.
Depending on how you tell the program to embark upon its search, it can identify only files that are identical based on content, or it can just find files with similar titles. In other words, Duplicate Cleaner will keep you from sending your boss the wrong copy of a file, which makes it downright essential.