“Humanism is a progressive philosophy of life that, without supernaturalism, affirms our ability and responsibility to lead ethical lives of personal fulfillment that aspire to the greater good of humanity.”
Humanists generally do not believe in gods, but Humanists include agnostics (who aren't sure) as well as atheists. Humanism has no dogma, or central authority, but one widely-recognized statement of Humanist aspirations is the Humanist Manifesto III (which starts with the sentence quoted above).
Other Humanist organizations of interest include:
(We will be adding links here over the coming weeks.)