Antispam
Markup: clickable email adresses - but with antispam
Makes email addresses clickabe, but obfuscates them to block spam harvester bots
Recaptcha
Enabling a recaptcha for commenting articles (You need to apply for a key)
Spam Protector (RBL)
Will reject comments made from hosts which are listed in RBLs. Pay attention that this may affect proxy-users or dial-up users.