Akismet — Download from WordPress Plugin Directory

What it does:

  • Helps filter out potential spam comments.
  • Comments that seem to be spam are held for admin to moderate or delete.

Requires:

  • Requires a free API key from Wordpress.com.
  • Already have an account with Wordpress.com? Sign in and look for your API key on your  Profile page.
  • Don’t have an account? Sign up for one. Select the Just a Username option if you don’t want to bother having a blog on wordpress.com.
  • More information on Wordpress.com API Keys.