Αντίο (antío)
Goodbye. (more final; for longer separations)

Γεια σου (geia sou)
Bye. (informal; to one person)

Γεια σας (geia sas)
Goodbye. (formal or plural)

Τα λέμε (ta léme)
See you. (very common)

Θα τα πούμε (tha ta poúme)
See you. / We'll talk. (common)

Καλό βράδυ (kaló vrády)
Have a good evening.

Καλό Σαββατοκύριακο (kaló Savvatokýriako)
Have a good weekend.

Καλή συνέχεια (kalí synécheia)
Have a good rest of your day. (literally: good continuation)

Καλή επιτυχία (kalí epitýchia)
Good luck. (especially for exams, interviews, projects)

Να προσέχεις (na prosécheis)
Take care. (informal; to one person)

Να προσέχετε (na proséchete)
Take care. (formal or plural)