Google Authenticator is a plugin for self-hosted WordPress installs that lets you require Google’s Two Factor Authentication application for access to WordPress.
I’m currently using it on this blog and have to enter a numerical code from the Google Authenticator on my phone very time I login to the admin area. The setup was trivial and it has worked like a charm.
The only drawback is that this renders your blog inaccessible from programs that are not set up to prompt you for a Google Authenticator code, such as the WordPress mobile apps for iOS and Android.
Enable the App password feature in the plugin, and You’ll be able to access your blog from mobile apps.