I don't believe in any gods, hence atheist.
but I'm not sure if the GNU philosophy is a "religion" as I agree with most of it. Well I still have M$ Windows, HL1 and NVidia's proprietary driver for GNU/Linux installed on my computer so I'm not a totally GNUisance
edit:
here is a funny comparation of different religions (no offense to anyone!):
http://www.gnu.org/fun/jokes/shit-happens.html