Come stai? = How are you? (informal)
Come sta? = How are you? (formal)
Come va? = How's it going?
Sto bene = I'm fine
Sto benone = I'm terrific
Sto benissimo = I'm very well
Sto molto bene = I'm very well
Sto abbastanza bene = I'm quite well, or I'm well enough
Sto cosi' cosi' = I'm so-so
Sto male = I'm badly
Non sto bene = I'm not well
Non c'e' male = Not too bad
Bene, grazie, e tu? = Fine, thank you, and you? (informal)
Bene, grazie e Lei? = Fine, thank you, and you? (formal)