My personal arguments against a Christian god:
1) If the Christian god is truly omnipotent, it would mean he would know everything--past, present, and future--therefore; when he made us, he had already known that things would go to hell (no pun intended). If god is benevolent, he would not have made us just to see his creation suffer. This includes the fact that he created a world that is naturally destructive and violent (e.g. earthquakes, tsunamis, volcanoes, hurricanes). Therefore, god is not moral, contrary to the Bible, so evil and suffering contradict existence of god.
Let's start at the beginning. If the Christian God is real, that means that He did in fact create a perfect world in the beginning. A world free of sin and suffering and death. But he gave us the ability to choose to follow Him or rebel and live against Him. He also gave angels like Lucifer the same freedom. His and man's choice to sin and reject God resulted in the world we live in today. Is this the way things will be forever? Hell no. This is merely a stepping stone in the abyss of eternity.
2) If God gave us free will, he would not have placed upon us the condition that we must worship him and no other god.
Well according to the Christian God, no other gods exist. So really, you've been given the free will to choose between God and eternal life or eternal death. This isn't like choosing between obeying your parents or rebelling and living your own life. This is really about choosing between good and evil.
In fact, this gives perfect justification for going to war in the name of the "right" god. In the course of history, when you realize how many wars were fought in the name of god, there is a question of why God would want millions to die for him if he wanted people to do good and right in his name.