Online Journalism Review has an interesting write up on the how Bloggers fight comment spam. The article, Bloggers Declare War on Comment Spam, but Can They Win?, talks about the chronology of events leading to this war and few rules of thumb to fight comment spammers.
Incidentially, I had more than 500+ spammed comments flooding my MT installation. More spams were coming in every day in lots. I had installed MT-Blacklist a month back. And I should say it is one of the best. Jay Allen, the developer of MT-Blacklist is a demi-god. MT-Blacklist fight spams like nobody’s business. It have literally taken out 98% of the comments that are spams. The in-flow of spams has also reduced drastically since then.
If you are looking for the best-of-the-best solution to comment spam, the practical suggestion, install a blacklisting service.