Spam can often be a problem for comments on blogs. A great way to stop spam on blogs is to remove the option for comments. Often Wordpress installations get deluged with comment spam used solely to link back to the spammer's site often selling nefarious products. Another option is to use a Custom CMS Web Design we so that spammers are less likely to find your site. If you must leave comments active you should have them moderated so they aren't automatically posted. Here is some wordpress plugins to help you manage the spam.

• Akismet is installed by default on your wordpress installs. It, however, is not activated by default. You will need to first go to plugins and activate Akismet. Then you will need to go to Akismet and sign up for an API key. It is free if you select the free option. Then go to your blog settings under Plugins then Akismet configuration and insert your key and save. Voila!
• Require Login is another way to block spam on wordpress installs. This will definitely block spam but will also de-sway one-time users from commenting on your blog. Go to settings, discussion and click the tick under requiring login for commenting.
• Recaptcha is the most common of the spam blockers these days. However sometimes they are people blockers too when the text is hard to discern for the average person. Search plugins from your install by typing in "WP-reCAPTCHA". Then install. You will need an api key for this too which you can obtain here.
• Trackback Validation is a plugin that blocks trackback pings that are created by bots. You can download it here 
• Referrer Bouncer is great as it requires no configuration so is a really quick install. It bounces refferer spammer bots and you can download it here.
• Antispam Image Plugin is easier for the user than recaptcha and just requires them to identify an image rather than mixed up letters on top of each other. You can get it here.