I am using Duplicate Finder to solve this problem...
Duplicate Finder is very fast in searching duplicate files with good interface. it does CRC32, byte/byte and Same FileName comparisons and allows you to batch mark and batch delete or move the dupes.
Main view shows all file details so you can combine that with a quick review to be sure you're not moving or deleting anything you don't want to. It also have popup resizable picture viewer to view picture files.
I really like Duplicate Finder. An especially nice touch was when it told me that I was deleting all copies of a file. I tried a few other duplicate file finders and hated them.
