Ranked in these QuestionsQuestion Ranking
Pro Tolerates multiple sessions
I often run multiple sessions of DoubleKiller Pro, to find duplicate files among different sets of disks.
Pro Flexible rules for finding duplicate files
The program can find duplicate files based on any combination of size, name, CRC, and byte-for-byte. It's possible to limit search to files matching a specific name or extension pattern (great for limiting search to certain file types) as well as using the same technique to exclude certain results. You can also tell the software to ignore any of combination of read only, hidden or system files as well as files of below or above certain size and archives.
Con No byte by byte comparison
While CRC checksums will be enough for most people, an option to check for duplicate files byte by byte would be nice.
[Edit] DoubleKiller does offer that option.