AllDup is a flexible tool that will quickly locate duplicate files on your system, and allow you to delete any that you don't need.
The program is supremely configurable. You can tell it which drives and folders you'd like it to examine, for instance (and it works happily with local and network systems). File and folder filters (inclusive or exclusive) make it easy to search for particular folders and file types only. And you can choose to compare files by any combination of name, extension, size, content, last modified date and more.
All these options don't seem to slow AllDup down, though, and the program generally delivered speedy results for us. Even when this isn't possible - you're scanning a huge external USB drive, say - it doesn't feel slow as the program delivers good feedback, with a progress meter revealing how much longer you'll have to wait, and how many duplicates have been found so far.
And once the process is complete, then you get a host of options to select particular files and delete any that you don't need. So many, in fact, that you need to be careful: delete something important and you could trash your PC. Pay attention and take the time to learn how the program works, though, and it'll help you analyse your hard drives and potentially free up a great deal of space.