Ohayo Gozaimasu - Good Morning (untill about 10am). Note the 'u' in Gozaimasu is silent.
Konnichiwa - Hello (from 10am to evening ... around sunset)
Kombanwa - Good Evening
Oyasumi Nasai - Good Night
Sayonara - Good Bye. Used with people you know or friends, etc.
Shitsurei shimasu - Very Formal Good Bye.
Ja Mata or Dewa Mata - See You or Well Then or Laterz...
Itte rashai - So long (actually it means, "Go and Come back"). This is said to the person when he leaves house. Like a wife telling Husband in the morning.
Itte mairimasu - So long (actually it means, "I am going and coming back"). This is reply of Itte rashai
Tadaima - I am back. Generally said by the person returning home.
Okaeri Nasai - Welcome back. Reply of Tadaima.
Omedeto Gozaimasu - Congratulations
O-daijini - Take care of yourself
Sumimasen - Sorry or Excuse me
Moichido Onegaishimasu - Can you repeat it please (when someone says something you dont understand)
Chotto matte kudasai - Wait for a moment please (said while trying to find something or thinking about something)
Ki o tsukete - Be careful or Take care
Abunai - Look out
Dame desu - No Good, Impossible