Do you have a Wordpress site? If so, there are plugins that catch most of the spam, you never even see it. Also, make sure that all comments have to be moderated before being published. That might be a problem if you get tons of comments but if you can handle it, moderate them first. That way, you can catch the odd one that gets through the spam catcher.
Another thing you can do is to add a captcha.
Another thing you can do is to add a captcha.
