Atheist vs. Humanist

There has been some discussion about the fact that not all atheists consider themselves Humanists. I, personally, consider myself both. When people ask my beliefs, I say "atheist" first and if in conversation try to get around to "Secular Humanist". The Humanist ideals describe the things that I do believe in and support. For those of you who do not have a god belief, yet reject Humanism, what are your reasons? Are we okay with labels that describe what we don't believe in? If not Humanism, then are their other positive philosophies that others subscribe to?