fdupes

This is a nice little tool helping to find duplicate files within a given directory.

1. compare the size of the files
2. compare their MD5 sums
3. if above matches, compare them byte-by-byte

Invocation is just as simple as eatin' pancakes:

fdupes -r -n /stuff

compares all files within /stuff recursively (-r) omitting zero-length files (-n).