Ask HN: tools to find patterns of data on disk?

I'm looking for tools (Mac OS X and /or Windows) to find data matching certain patterns on my disks. I would use this to ensure I don't keep "sensitive" data after working for a given client, for instance. Are there any particularly useful tools to achieve this, before I go find/grep/sed all the way ? Note: I don't need to scan unusused space (which I can 0-purge), but scanning archives (zip/7z etc) would be useful. Thank you!