Γεια σου (geia sou)
Hi / bye (informal; to one person)

Γεια σας (geia sas)
Hello / hi (formal or plural; to more than one person)

Καλημέρα (kaliméra)
Good morning / good day (used until early afternoon)

Καλησπέρα (kalispéra)
Good evening (used from late afternoon/evening)

Καληνύχτα (kalinýchta)
Good night (said when going to sleep)

Τι κάνεις; (ti káneis?)
How are you? (informal; literally: What are you doing?)

Τι κάνετε; (ti kánete?)
How are you? (formal or plural)

Πώς είσαι; (pós eísai?)
How are you? / How are you doing? (informal; more about how you feel)

Καλά. (kalá)
Good. / I'm fine.

Πολύ καλά. (polý kalá)
Very well.

Μια χαρά. (mia chará)
Great / just fine (very common, casual)

Έτσι κι έτσι. (étsi ki étsi)
So-so.

Δεν είμαι καλά. (den eímai kalá)
I'm not well. / I'm not doing well.

Όλα καλά. (óla kalá)
All good.

Καλά, εσύ; (kalá, esý?)
Good, and you? (informal)

Καλά, εσύ; (kalá, esý?)
Good, and you? (informal)

Χάρηκα. (chárika)
Nice to meet you. (literally: I was glad; also: pleased)

Χάρηκα πολύ. (chárika polý)
Very nice to meet you.

Καλώς ήρθες. (kalós írthes)
Welcome. (informal; to one person)

Καλώς ήρθατε. (kalós írthate)
Welcome. (formal or plural; to more than one person)