hence the redundancy check with CD Check (worth noting that it doesn't do audio disks...) - it's a handy tool and you can compare against a directory or a hash file (it will also generate the hashes)

That does sound nice.

At the moment I'm using the Non-Duplicates search feature of NirSoft's SearchMyFiles and that seems to be pretty good.

FWIW I usually include a copy of the hash file in my write

Sounds good -- I guess if that's not too big, one could store multiple copies for the unlikely case of the hash file getting corrupted...