"I create meaning for my life"
You often hear this from atheists explaining how it is that they live without any sort of higher purpose. It usually means something like "I have found something I love to do, and I have devoted myself to it. I need no more 'purpose' than the ability to do what I enjoy." Usually there is a subtext of nobility to their explanation, implying that their creation, their willing of purpose exhibits an inner strength not possessed by those who (must) look outside themselves for purpose.
I think I've found the root of this idea in Nietzsche's Thus Spoke Zarathustra. Zarathustra, the prophet Nietzsche chooses as mouthpiece for his message, preaches the coming of the overman, a breed of human which, having cast off the values of Christendom, embraces the body and the will as primary and regards any attempt to transcend them as weakness:
A new pride my ego taught me, and this I teach men: no longer to bury one's head in the sand of heavenly things, but to bear it freely, an earthly head, which creates a meaning for the earth.
A new will I teach men: to will this way which man has walked blindly, and to affirm it, and no longer to sneak away from it like the sick and decaying.
Also, a little later:
May your virtue be too exalted for the familiarity of names: and if you must speak of her, then do not be ashamed to stammer of her. Then speak and stammer, "This is my good; this I love; it pleases me wholly; thus alone do I want the good... Once you suffered passions and called them evil. But now you have only your virtues left: they grew out of your passions.
The meaning which the overman creates for himself is a supreme act of will in which existing cultural values are re-valued. Virtue is that which is chosen, freely and unconstrained by cultural norms, from within oneself. The "thou shalt" is nothing and the "I will" is everything.
This is the radical individualism out of which meaning-creation was born. For if the will creates meaning, what else does it create? what doesn't it create? Is there anything to which it is subordinate?
Nietzsche's answer was "no", and it led him to envision a world led by men who are their own highest good.
 I can't resist interjecting personal commentary: I find this idea that one can life a fulfilling life by just doing what he happens to like highly insufficient and not even very thoughtful. Classical paganism is light-years ahead and far preferable. The Greeks and the Romans understood that man has a nature - that there are certain things which are true of us whether or not we want them to be. They understood that education was necessary to train the faculties to appreciate the highest goods, and to live the best life. He who spurns this teaching in order to follow his own will foolishly disregards the wisdom of the ages on what kind of being man is, what his limits are, and what can make him happy. He does so to his peril.
 Incidentally, there is a fantastic series of posts on Jim's blog under the title Thus spoke the Platypus. It's a brilliant way to response to Nietzsche, loosely parodying the style of Thus spoke Zarathustra. The most recent installment is here.
Thus Spoke Zarathustra book I, speeches 3 and 5