Comment Moderation is very effective in addressing unwanted comments. The best defense against comment spam is just watching your comments.
Still if your blog is popular among people it will be popular among comment spammers as well and you may not be ale to do the heavy lifting all by yourself.
Luckily there are some great tools that can help. Akismet which comes installed with each of our WordPress hosting plans is a great service. Just sign up at http://akismet.com/ and send us the API key and we can do the rest.