Italian	English
Ciao!	Bye! (friends)
Arrivederci! / ArrivederLa!	Goodbye! / Goodbye! (formal, to one person)
A presto!	See you soon!
A dopo! / A domani!	See you later! / See you tomorrow!
Ci vediamo!	See you!
Ci sentiamo!	Speak soon! (by phone or message)
Buon viaggio!	Have a good trip!
Grazie di tutto!	Thanks for everything!

Ci vediamo and ci sentiamo are literally we see each other, we hear each other — the present standing in for a near future. Add a time to make a plan: Ci vediamo sabato!