One of the awesome ideas behind blogging is the ability to allow feedback in the form of comments. Unfortunately, 2 in 3 comments are spam. So a number of solutions have been made available that combat spam in different ways, however, some methods can really annoy your users and limit long-term feedback.

• Captcha - Also known as "those pesky graphical images that you can hardly read." Captcha solutions work quite to stop spam but only when implemented in the correct way (as we learnt from Mustlive’s recent Captcha bugs of the month project). The major downside to Captchas is that they bug me and probably most people. Who the heck wants to get their glasses on and squint to read some graphic image every single time they want to leave a comment.
• Authentication - Having a user register before allowing them to make a comment. Unfortunately, automated programs can usually do this automatically, so Captcha systems are usually now implemented along side this process. At least we only have to enter the Captcha once now, right? Yes, but now I have to login every time I want to leave a comment! That means having to remember another password! OpenID may be the way forward in this area.
• Blacklist - Many software packages allow blacklists. This means we can block comments based on "BAD" words. I don’t know if you’ve ever been to a live game between Arsenal and Manchester United? Lets just say there are so many ways to say the same thing. Blacklists are good when implemented with other methods but certainly not as a standalone service.
• JavaScript - BlogSecurity’s SpamBam uses client-side scripting in your browser to ensure that your user is using a valid browser. This is currently a very effective method to prevent comment-spam as most spammers use automated programs that don’t have JavaScript support. I quite like this system, although I feel this could really be an awesome approach but more work is needed on the plugin.
• Smart Checks - These are generally Spam systems like Akismet. They use a variety of checks and a chain of blacklists to check whether the comment is spam or not. Great for general use, however, it means that all your comments have to be sent to a third party server. This can cause excess traffic.

I hope this helps you choose the right system for your blog.