Well, to take a page out of Plato's book...
Plato says that the meaning of life is to be happy. However, you are trully happy only when you are a just person, and even the most unjust person can never be as happy as a just and virtuous man. (Hey, I'm at a Liberal Arts college. If my friends ever saw this, and they didn't see me using some philosopher we studied, they'ed have a fit)
Personally, I see the purpose of life as to be virtuous, because then everybody benfits. And I do agree that by being virtuous, I am happy, not only in some next world, but in this world as well.
I am a Christian, but I've had this general view for a long time before I was a Christian. That said, this topic in general will eventually become a discussion on religion if we aren't very careful.