...or C) limit comment rights to a group of responsible, traceable people

...or D) moderate new registrants for a probationary period

...or E) enlist some of your users-in-good-standing for moderation

...or F) moderate just those comments which an automated system flags as having high spam likelihood (links, images, emails)

...or G) require some small demonstration/forfeit of value (such as a posting fee) for each post. (Risking a non-probationary account that took effort to create is a special case of this.)

...or H) blended variants of the above