The most common I use are Heya, Hiya, and Aloha. You could look up all kinds of foreign ways of saying hello and memorize them to impress your friends. If you're going for humor, you can use famous lines from movies or characters. My favorites include "Hey there, Hi there, Ho there" From Mickey Mouse Club, "Howdy, Howdy, Howdy" from Toy Story, and "Hiya Pal" from Mickey Mouse himself :)
Well, my favorite "funny" way to greet people is to say in my best "Joey" from Friends voice, "How you doin?" Sometimes I use "ello mate", or "Chello" from "JJ" of Good Times", and sometimes use "Nanu Nanu" in my best Mork voice.