There are many things for which we owe the Greeks: democracy, geometry, the marathon. Not to mention souvlaki, moussaka and baklava. But arguably the most valuable asset to any person: wisdom.
Indeed wisdom is synonymous with Greece -- the cradle of Western thought is traced to the ancient Έλληνες. Of all the wise philosophers, seven were distinguished from the early 6th Century BC and bestowed the title of "The Seven Sages."