I don't feel a need for an atheist tee anymore, but I'm a fan of both Sagan and NDT, even though neither were/are self-described atheists. I would love a Sagan head tee or a an NDT Pizza "done in seven seconds (or some such thing)" tee.
"For me, it is far better to grasp the Universe as it really is than to persist in delusion, however satisfying and reassuring." - Carl Sagan