Best Free Duplicate File Detector

I must confess that I'm not a great fan of the practice of routinely deleting duplicate files from PCs. Sure it can free up some disk space but it can also get inexperienced users into a great deal of trouble. There are quite a few duplicate file detection utilities around but CloneSpy is the one that impresses me the most. It's certainly not the fastest program in its class but it's definitely the smartest.
First, you can specifically select what is to be scanned and this can include multiple drives, multiple folders or just individual folders. Second, it has the ability to detect duplicates by CRC, by file name, by CRC and file name and by file name and size. Third, it will also detect zero length files. Fourth, the program does not need to be installed but can be run from the executable so it's a good candidate for your USB Flash drive toolkit. Finally, it throws up duplicates to the user in a way that at least makes you think about what you are deleting. Click-happy users may find this latter feature an annoyance; to me it's a safety feature. Safety feature or not, please read the help file and use with care. In particular do NOT include your Windows folder in your scan unless you are a knowledgeable technical user.

Code:
Freeware, Windows 98 and later, 643KB.
http://www.clonespy.com/