I’ve just activated a strong auth system to access this blog as Administrator.
It is a system we also use where I work and it is amazing for the simplicity and security blend that it adds to the authentication process.
They have huge integration with a number of systems and technologies, and you can find WordPress specific one here.
It is free up to ten users, but also paid versions have negligible prices (like 1$/user/month).
It really rocks for usability and strength of auth process.