Formal:
* "Bonjour, oui ça va bien, merci. Et vous?" (Good morning, yes I'm fine, thank you. And you?)
* "Bonjour, je vais bien, merci. Et vous-même?" (Good morning, I'm well, thank you. And yourself?)
Informal:
* "Bonjour, ça va super! Et toi?" (Good morning, I'm doing great! And you?)
* "Salut, ça roule! Et toi?" (Hi, things are going well! And you?)
* "Bonjour, plutôt bien, merci. Et toi?" (Good morning, pretty good, thanks. And you?)
* "Bonjour, tranquille, merci. Et toi?" (Good morning, I'm relaxed, thanks. And you?)
Adding a little extra:
* "Bonjour, ça va bien, merci. J'ai passé une bonne journée/soirée hier." (Good morning, I'm fine, thank you. I had a good day/evening yesterday.)
* "Bonjour, ça va, merci. J'ai hâte de... (mention something you're looking forward to)." (Good morning, I'm fine, thank you. I'm looking forward to... (mention something you're looking forward to).)
Adding some humor:
* "Bonjour, ça va comme un lundi matin! Et toi?" (Good morning, I'm feeling like a Monday morning! And you?)
* "Bonjour, j'existe encore, c'est déjà pas mal! Et toi?" (Good morning, I'm still alive, that's something! And you?)
Remember to adjust the level of formality based on your relationship with the person you're talking to. If you're unsure, it's always better to err on the side of being polite.