Well... some musics, also when i go out with my friends, sometime we only talk when we go out, or i spent all the day playing videogames with one of my friends, still that's really fun, i really like to be with my friends
Reading/watching/playing a great story (as in, book/film/TV series/game) and getting to that really epic moment. The final fight, the rallying cry, the one moment of awesomeness that just makes you cheer and woop and just... Yeah. Examples include (but of course are not limited to): Mass Effect 1, when Commander Shepherd gives an awesome speech to her crew after becoming a Spectre; Zone of the Enders 2, the final fight against Anubis; and Tengen Toppa Gurren Lagann. Just, all of it. Forever.
A more sedated option (though no less joyful, I believe) is simply when I make a friend happy. If I can do something for them and make them happier, then I am happy as a result.