OK, I give up. The spammers have won for now, and I am blocking all comments unless from a registered user. I tried a spam filter and it didn't work, I tried having unregistered users comments be moderated, but today I have 62 pages of comments to sift through... so until I can come up with a better method, you will have to register to leave comments I'm afraid.

Bastards.

EDIT: Maybe I will win in the end, I have found a better anti-spam module for Drupal and will see how good it is - but for now, comments will remain off limits to anonymous users.