"Hey" "Good morning/afternoon/evening" - These are more friendly if you remove "good". "G'day" - Informal. It used in Australia and New Zealand, but it's very rarely used in the cities. "Howdy" - Stereotypical of the US south, though I'm not sure if this is actually used there anymore. "Yo." - Extremely informal. "Hi"

adding to Jmat's list... "Greetings" - mostly used in formal written correspondence "sup" - very informal, short for "what's up" "Look what the cat dragged in!" - very informal and teasing. Used when greeting someone who is sick. Use carefully it can mean a person doesn't look their best.

hi