Formal:
* Buongiorno, bella. (Good morning, beautiful.)
* Ciao, bella. (Hello, beautiful.) - This is more common than "buongiorno" in informal settings.
Informal:
* Ciao bella! (Hey beautiful!)
* Bella! (Beautiful!) - This is very informal and might be considered flirtatious.
* Sei bellissima! (You are beautiful!)
It's important to remember that "bella" is a very direct way of calling someone beautiful. If you are unsure of the context, it's always best to err on the side of caution and use a more general greeting like "ciao" or "buongiorno".