While Selyd gave you a lot of (too many in my opinion) options, most of them are archaic (old, not used anymore). Practically in today's Ukraine you will do well with:
Привіт! - Hello (informal)
Добрий ранок/день/вечір - Good morning/day/evening (formal)
And that's it :)
Also, young people often use English greetings like хай (hi), or йоу (yo - very informal, for friends and young people only)