Greetings and Farewells
Ongi etorri – Welcome
Kaixo – Hello
Aupa – Hey 
(Also used to cheer people on, as in a race.  The equivalent of “Come on!”)
Agur – See you later
Egun on – Good morning
Arratsaldeon – Good afternoon
Gabon – Good night

Courtesies
Mesedez – Please
Barkatu – Excuse me
Sentitzen dut – I’m sorry

Eskerrik asko – Thank you 
Zuri – (Thanks) to you (The equivalent of you’re welcome)
Ez horregatik – You’re welcome
Berdin – The same to you

Well wishes
Ondo pasa – Have a good time
Zorte on – Good luck
Zorionak – Congratulations! (Used for celebrations like birthdays)

Responses
Bai – Yes
Ados – Ok
Agian – Maybe
Ez – No