Speak in Silence
Learn sign language. Learning any foreign language is Neurobically stimulating, but learning American Sign Language (ASL) is especially so. Signing requires your hands (and the parts of the cortex that control them) to do something completely new: be responsible for communication. And your visual cortex must learn to associate particular hand positions with meaning, forming links to the parts of the cortex responsible for language and communication. Sign language is challenging, complex, and rich, and requires integrating new types of sensory information to take the place of the usual auditory associations. If you do learn some sign language, you will also be able to communicate with the hearing impaired in a much richer way than when they are reading your lips.
Communicate a thought or idea to someone without using your voice. Playing charades is one fun way to do this, and both actor and guesser benefit.