Formal/Polite:
* Taisez-vous! (Formal, imperative, meaning "Be quiet!")
* Silence, s'il vous plaît! (Formal, meaning "Silence, please!")
* Chut! (Informal, meaning "Hush!")
Informal/Direct:
* Ferme-la! (Informal and rude, literally "Close it!" - often used by males)
* La ferme! (Informal and rude, literally "Close it!")
* Tais-toi! (Informal and rude, meaning "Shut up!")
Other options:
* Arrête de parler! (Meaning "Stop talking!")
* Assez parlé! (Meaning "Enough talk!")
Important Note: "Shut up" is considered very rude and aggressive in French. It's best to use the more formal and polite options, especially if you don't know the person well.