Handling spam

I setup a blog for a friend of mine. He didn’t want to force people to register or to moderate the comments. He wants everyone to be able to post either positive or negative comments. The issues is, he is now getting tons of spam in the comments.

Everyday I’m logging in and either deleting posts that are strictly spam, or tagging them as spam. This has become very time consuming for me. What is the best way to handle spam, but still allow individuals to freely post comments?

My thoughts are that we will have to start registering individuals and possibly start moderating the comments. Are there other thoughts and idea’s?

Thanks.

Daryl