Here is a list of webpages and resources that you can access for FREE about the arguments against the existence of God! Here you go:
20+ Questions for Theists. Jeffrey Jay Lowder's list of questions for believers which reveal a number of arguments for atheism and expose a number of flaws in theistic arguments. It's a brief but highly recommended blog.
Ebon Musings: The Necessity of Atheism. This is a very good page with excellent summaries of the evidential arguments for atheism. That is, the author shows how various things about the universe make more sense if God does not exist than if he does.
Closer to Truth: "God." A series of interviews with philosophers and scientists who explain, in common-sense terms, what they think about the arguments for and against the existence of God.
Internet Infidels: Evidential Arguments for Atheism. Internet Infidels has essays written by a broad variety of critical thinkers arguing that atheism is better justified by various pieces of evidence, including Darwin's theory of evolution.
Internet Infidels: Logical Arguments for Atheism.
Theodore Drange: "Ten Atheistic Arguments" and "A Survey of Incompatible Properties Arguments." A veteran philosopher goes over some of the arguments for God's nonexistence, the first simply being all kinds of arguments for God's existence and the second being a review of arguments for incompatible properties (incompatible properties arguments try to show that the very definition of God is like a square circle; God is defined as having two different properties which could not possibly exist in the same entity).
Evil Bible: God is Impossible. It's a tad simplistic and mainly focuses on the God of the Bible, and I would recommend checking the scripture references in context, but other than that it is good food for thought.
Richard Carrier Blogs: The God Impossible. Richard Carrier goes over his thoughts on why God is impossible. Very interesting and often unheard arguments are brought out.
My Arguments for Atheism.
1. Bodiless Minds Probably Cannot Exist. What if someone told you about a chair that wasn't made out of anything. That is, not simply a chair that was made of a different sort of matter and energy than you are familiar with, but a chair that wasn't made out of anything at all. Do you think that such a hypothetical chair is even possible or at all sensible? I don't, and I suspect most people agree. However, most people seem to think that it is sensible to talk about spirits, souls, and gods, all of which are minds that are not made out of anything at all. However, philosophers and neuroscientists have long been thinking of our human minds as being completely physical in nature. Human minds are like snowflakes: just as snowflakes are made of many water-molecules arranged in a certain pattern to create the snowflake, so too are human minds/brains just a collection of brain cells arranged in a certain way to function as the people we are. When we describe who someone is, we describe them in terms of what they do and how they react in certain situations, and these are all fundamentally just "higher-level" descriptions of how a collection of matter and energy behaves. At the microscopic scale you see the water molecules (that is a "low level" description) but if you zoom out to the macroscopic scale you see the snowflake (a "higher-level" description). This is how people are: at the microscopic level you have cells and how they behave, and at the higher-level scale you have people and how they behave. Seen this way, it makes no sense at all to speak of a person who isn't made out of anything or about any mind without a body. Perhaps this is only a hunch and does not, in and of itself, prove with very much certainty that bodiless minds cannot exist. But it does lend support to the idea and provides a good ground for formulating the hypothesis that minds cannot exist without bodies. So let's see how that hypothesis fits the evidence.
The fact is that we have no rock-solid evidence of any sort of mental activity or signs of conscious awareness that occur without the activity of a physical brain. We could have had such evidence. We could have had evidence of a poltergeist, a genuine demonic possession, psychics who can truly communicate with the dead rather than relying on cheap parlor tricks, Near-Death Experiences could have proven to be genuine experiences of the mind outside of the body (see Keith Augustine's article as well as Victor Stenger's excellent chapter on the subject in The End of Christianity), we could all have memories of experiences from before our physical body came into existence (past lives, or God briefing us on our mission before he sent our souls into earth-bound bodies). We have extensive evidence that the human mind is the brain, as I've discussed on page 97 of my book Atheism and Naturalism and as Steven Conifer has discussed here. Of course, the absence of evidence for bodiless minds combined with the abundant evidence that minds require bodies provides astonishing and rock-solid support for the philosophical hunch that I discussed above. I'd go so far as to say that it is very likely that bodiless minds cannot exist. If it is very likely that bodiless minds cannot exist, and God is defined as a bodiless mind, then it follows that it is very likely that God does not exist. This argument wipes the floor clean of all possible gods, even a deist god who doesn't care about us and never does anything. Though such do-nothing gods cannot be disproven by evil or by a lack of evidence, because they are part of a category (bodiless minds) which probably do not and can not exist, so too do they not exist.
2. Evil and Evolution. As I once put it: Atheism makes the distinct predictions that the only way complicated living things will exist is if evolution occured (because on atheism there's no person to create them, they can only be products of nature) and that the world will contain injustice and evil, simply because atheism means that there's no perfect being running the universe, and without such a person, it is overwhelmingly likely that bad things will happen from time to time. And that's exactly the universe we live in.
For those who doubt evolution, see The 29 Evidences for it, or Why Evolution is True or The Greatest Show on Earth or chapter 10 of my book, Atheism and Naturalism.
For those who doubt the argument from evil, let's take on the most popular objection: free will. I read an article by local pastor on the problem of evil and here are some excerpts from it that I think are revealing:
"One night, a 16-year-old teen awakened to find a stranger in her bedroom. He held a knife to her throat. He told her to be quiet or he would kill her and her parents down the hall. Then he took her outside and raped her. All the while she was praying, telling him he did not have to do this and that God would forgive him. He didn’t stop. When he was done, he let her go back to her home. But she could never get back to her unspoiled life."
"Why does God allow things like this to happen? ...Theology talks about God's perfect will, which is that all live in happiness and fulfillment. Theology also talks about God's permissive will, which allows human beings the freedom to fail. To have a real victory, there has to be the possibility of failure. In order for us to follow God voluntarily, the possibility also has to exist to reject God's will."
If you had been there the night that this 16-year-old girl was raped, wouldn't you have tried to stop it? Or would you debate with yourself over whether allowing the girl to be raped was better than allowing the rapist his free will? I would have fought for the girl without a second thought, and I'd even go as far as to say that anyone of any moral fortitude would do the same. So if you believe that the protection of the girl is more valuable than allowing the rapist a freedom of choice, then you cannot believe in God. Because God is supposed to be a being with enough power to stop these things from happening, and also completely good, which means that if he existed he would have done the right thing and prevented the rape, even at the cost of destroying the rapist's free will. Events such as this leave us with no choice at all but to reject the sorry, soft, illogical pat answers of the preachers and theologians and look at reality for what it is: without a god.
3. Absence of Evidence. There's no good evidence for God, and if there was a God that isn't what we would expect. A good God would make sure people knew the truth because it is good to know the truth.
4. Postulating a god violates Ockham's Razor. Postulating that only the universe exists is simpler than postulating a universe plus a god. Since simpler theories are to be preferred (everything else being equal), then we should not believe in a god.
5. The Argument From Design for the Nonexistence of God. Believers often point out that if the orbit of the Earth were ever so slightly closer to or further from the sun, life couldn't exist. They pile up a number of very specific conditions which must coexist in order for life to exist, and ask why our planet is this way rather than any one of the millions of other ways that it could be which would not allow for life to exist. They're wrong that this points to God, as there are so many trillions of planets that it is no miracle that at least one (if not millions of others) should have life. Back to the point I was making: Believers ought to ask why God is exactly the way he is rather than some other. If there is an uncaused immaterial mind that exists (and only one of them, not many, which would commit us to polytheism) what are the odds that that mind would be absolutely perfect instead of one gazillions of ways it could be imperfect? Think about it: If my mind were altered just a bit by slicing out a piece of it or altering its structure with drugs, injuries, etc. I would probably be insane and/or mentally retarded. It does no good to object that my brain is physical while God's mind isn't, after all, we could imagine (if such things are possible, and I'm not sure they are, see argument 1) an immaterial version of every insane/idiotic/demented mind that could possibly be. Why a perfect mind rather than one of those? There is no good reason to see one as more likely than the other, and so using the believer's logic which they were only too happy to use about our life-friendly planet, it must be no more likely. Stop and think about how many possible minds there are: there are at least 7 billion human minds, billions more animal minds, plus the minds of imaginary characters, and so on and so forth. By a conservative estimate, the prior probability that an uncaused mind would be a perfect one is one out of a hundred billion, probably much more.
6. The Big Bang Argument for the Nonexistence of God. My last argument is closely related to the previous one. If we were to postulate something that was not caused, what would it be like? Out of all the possible arrangements of matter and energy that there are, most of them would have to be very “random-looking.” If no one created the universe then no one chose what the first arrangement of matter and energy would be, it would be very random and chaotic. And this is exactly what modern cosmology tells us the early universe was like, just read about the Big Bang theory.