Verified answer

I know of Easy Duplicate Finder - it scans for duplicates for free. But I think you have to pay for it to delete all duplicates.

I am using Noclone duplicate files finder paid version. I remember it provide free version, but it may have some limited.

Glary Utilities

http://www.glarysoft.com/

Use caution though, it may find files in App Data and a duplicate in Programs and prompt you to delete one which may render your application useless.