Though this question can never be definitively answered as no one has ever seen proof that there is or isn't a god, I think that the question is worth exploring and is important when looking at your own faith. As a believer in God, if you do not ask yourself this question at least once, then the strength of your faith is questionable. It is a mark of good, strong faith to be able to ask these important questions and come out on the other side with an even strong faith. Otherwise, faith is blind.
That being said, it is my belief that God, or the concept of God in Western traditions, is an invention of men. There are many reasons that I believe this and I will expound upon them. First of all, all of the religious texts were written by men. The Bible, The Torah, The Qu'ran, all written by men, by humans just like the rest of us. They are said to have come from God, that God spoke to the writers of these books, but there is no definitive proof. It is all in what you believe. Furthermore, the teachings in these books, that are said to have come from God, often reflect the agenda of men. For this reason, there are countless wars fought over religions.
Secondly, God is an anthropomorphic figure with emotions, exhibiting the love and compassion, and the wrathful fury of humans. Why would an omnipotent and perfect being need emotions? Man made God in this way in order to feel a stronger connection to "Him". A God that you can talk to and imagine in your head is much more palatable than one who has no form or personality. This is why the Romans and Greeks had so many gods that expressed jealousy, lust, greed, and so forth. So that they could feel justified in their actions. Having a warlike God with human emotions makes man's agenda, no matter how atrocious, justifiable.
If this God were really superior to us, and worthy of our adoration, "He" would not have the same pitfalls as humans. For this reason, instead of God being a personal, human-like being, I submit that it is formless, emotionless, having no agenda. God is everything. Though, the idea of God being a tangible being is comforting, I think that this idea is flawed and leads to human beings thinking that they are superior to every other being on the planet. Also, it leads to races thinking that are more superior than others because they are God's "chosen people" and made in his image. Instead, I suspect that God was made in man's image for egotistical reasons and has continued on to this day for those very reasons.