If I just want to find and delete dupes quickly, I use CloneSpy
If I need more fine control over what I'm doing, I use AllDup
Both are Free for non-commercial use.
Both can handle any kind of file to find exact dupes. AllDup has some tools and options to make dealing with similar files a bit easier (file preview and the ability to pass files to a program for comparison, etc).
Both programs also allow you to move "deleted" files to a folder rather than actually deleting them which you should ALWAYS do to avoid disastrous mistakes (although making a full backup is even better).