Does gog.com offer any checksums (md5, sha1, or even gpg signature) for files offered for download? If so, where can they be found?

I don't know whether GOG offers anything like that, but ConnieThunder maintains a database. See http://www.gog.com/forum/general/the_what_did_just_update_thread/post10366.

thanks

officially there are none .... have been requested since so long, i don't have high hope. :/

there are multiples community requests about this

just folllow the link given by mrkgnao, it's possible not all hashes ain't up to date; but that's the best database to my knowledege you will find.

Hmm, when a game consists of more than one file, then the installer makes an integrity check, so I guess that there is indeed some kind of checksum involved.