Atheists get angry when one points out that they hold to a non-diety religion. But their's is a belief based upon at least as much faith as any "normal" religion.
Firstly, not everyone means the same thing by the word 'religion.' (Or by the word 'atheist,' for that matter.)
Secondly, if you define religion as belief, then all beliefs are religious--including the belief that the Sun will rise the next morning. Think of what that definition would do to the scope of the First Ammendment's guarantee of Freedom Of Religion.
Thirdly, both atheism and science are fundamentally different from religion (as I define those terms, at least): Both science and atheism are subdomains of an epistemelogical paradigm where there are no absolute beliefs. Scientific theories are not absolute beliefs that must be taken on faith--and that's true by definition.
By definition, a scientific theory (belief) must be falsifiable. Scientists must accept that, in principle, any of their theories/beliefs might be wrong, that new evidence may require that any belief/theory be discarded. Some even have begun to realize that the rationalist epistemology itself must also be falsifable (subject to the possibility of disproof, at least in principle.)