(It's been a few years since I've been in school, so hopefully my memories of what I was taught are correct... This was an argument from one of my professors that I always found interesting. Just throwing it out here for another viewpoint.)
According to the teachings of Thermodynamics, everything in nature is subject to entropy, which indicates that nature has a tendancy for disorder, since the more ordered the system, the more energy required to "assemble" it. (which is easier, throwing bricks into a pile or neatly stacking them?) This goes against the grain of the theory of evolution. Higher-order life forms such as humans (according to the laws of entropy) should be disevolving. (Of course, some might argue humankind IS on it's way down...)
So, if everything started from the "Big Bang", then who lit the fuse? I once had a religous studies professor who remarked that religion for many serves to fill the void of what can't be explained. This brings up another loaded question: So, when humans feel they have become enlightened enough to explain everything on the merits of hard science, will religion still exist? (Wow, how the course of this thread has changed!)