I've tried my best (with varying degrees of success) to avoid being an overbearing atheist; I don't want it to seem like I'm proselytizing. But I don't mind sharing my opinion when asked.
However, if a person has pondered the origin of their existence the idea of a God(s) comes into play.
I'd agree with this, and it's one reason that I am especially sympathetic with Deists (admittedly, I see deism as mainly filling a gap in a philosophical system; though if someone can get something positive out of it then I think that's great). At this point, science hasn't really been able to give a solid answer, so in that way some type of divine creator is no less likely than the idea that we have just always been here. However, part of the problem is then figuring out what type of God that would be, what evidence we have, etc., and I personally don't find holding to a non-personal God to be of much help. So, based on the evidence that there is, I just don't personally believe that there is a God, though I admit that someone could look at the same evidence and come to a very different conclusion.
I would be interested in hearing how you have reasoned that there is no God.
Well, to the extent that I've thought about it, most of the thought has gone into considering the evidence for a personal God, such as the one Christians worship. This, for me at least, is a somewhat seperate question from why I am not a Christian (which I gave some thoughts on
here). I've thought about this question in two ways: the first way was to assume that there was a God and then I tried to prove that there wasn't; the second ways was to assume that there was no God and then I tried to prove that there was. Without going into all the details (which would make for a very long post), if it's ok with you, I'd rather just leave it at the following bit.
When I tried to prove that there was no God, I found that I could not prove it, but that I thought there was a lot of evidence against something like a personal God, including things like the problem of evil, and the lack of a system/group which (only in my opinion) gives an adequate accounting of this possible God. When I tried to prove that there was a God, I found that none of the arguments (again, only in my opinion) really withstood criticisms against them. There are some very good arguments for the existence of a God, such as the design argument and the anthropic principle. There are arguments against these good arguments in favor of God, though, and I could go either way on those as stand alone issue. But, when I put everything, I first came down in the agnostic camp, and eventually went ahead into atheism.
Earlier I assume that you believed that Jesus Christ (besides being a historical figure) was the Son of God since you were an Orthodox Christian. Do you still believe that He as a man lived?
Yes, I did believe that he was the Son of God and God the Son, and I do still believe that he was an actual person who lived. I do think that some of the Christian apologetics are exaggerated, such as the claim that there is more historical evidence proving the existence of Jesus than any other figure in the ancient world. I also think atheists are really reaching when they say unequivocally that Jesus did not exist. How in the world do you prove with full assurance that a certain man did not live two thousand years ago? You can't possibly be sure of that type of thing; the best case for such a claim would be for there to be multiple contemporary sources which said that there was no Jesus, but there are no such sources. I will admit that I was somewhat uncomfortable with the way that the divinity of Jesus and the Holy Spirit was articulated/clarified, coming as it did centuries after biblical times. I can remember thinking to myself, when I converted to Orthodoxy, that if I went by the Bible alone I wouldn't be a Trinitarian, or at least I'd be agnostic on the topic. I took that issue, like many others, on faith.
And if you do believe there was a man Jesus of Nazerath...do you now think that he was a liar, a con-artist or just insane?
Well, I see that CRCulver and DavidBryan has already brought up what I was going to say here. I think that Jesus lived, and that the Apostles (and some later converts who were not eye witnesses), writing anywhere from ten to sixty years after the death of Jesus, wrote what they honestly believed happened. So for me, it is more about whether they got the stories straight, and how they got the stories correct. First, I'll say that I don't trust eye witness accounts further than I can throw the eye witnesses. I think psychology, and for that matter magicians such as James Randi, have shown pretty well that people see what they want or are inclined to see, and remember what they want or are inclined to remember. This is not to imply and intent to deceive, by "want" here I don't mean that they are trying to shape reality, it's just what often happens. Thus, you might have two eye witnesses who witness an auto accident, and both of them are perfectly sincere, but yet they completely contradict each other.
Second, there was quite a bit of time for redactors to even out any contradictions between the Gospels, which admitedly were circulated rather early as a set of four. Again, I do not mean to imply that they had some bad motives; for example, they may just have assumed that the copyist before them copied things wrong, and that they could correct things. While much is made of the Jewish precision in copying, I've read that most biblical manuscripts are riddled with mistakes, showing that exactitude in copying wasn't necessarily a high priority. Third, there seems to still be some minor contradictions, for example whether the money changers/Temple incident happened at the beginning of the ministry of Jesus or at the end. Maybe the proposed solutions for these passages are correct, but at this point I still have doubts. And fourth, we know with certainty that some passages were added to the text well after the biblical authors wrote the books, such as the famous story of the prostitute caught in adultery in John 8.
I think the Jesus Seminar type people go too far in their assumptions about what was not in the original. However, I do have doubts as to whether the Bible as we have it is accurate in it's historical, practical, and theological details. And, as an atheist, I don't believe all the stuff about miracles. I don't know whether it was Jesus doing what we would consider magic, or it was the Apostles misremembering or later attributing to Jesus miracle working out of reverence, or maybe it was meant to be more of a spiritual lesson than historical fact (as I think almost all the stuff in the Orthodox lives of saints is). I am inclined to assume that the central elements of the teachings of Jesus were really his, especially the ones which were derived from earlier Jewish sources (e.g., love God with all your heart, do unto others as you'd have them do unto you, etc.)
Anyway, I hope that provides some info on where I'm coming from. And, if you don't mind me asking, what do you think of what your husband says? And how does he take your own thoughts on this stuff? I live with a Christian wife, and I've found that it can be very interesting, and helpful, to discuss this stuff with each other. There is no pressure for either to convert to the other's beliefs, it's just a way of sharing who we are and where we are in life. I hope you are in a similarly civil and helpful situation.

DavidBryan
Fwiw, some thoughts...
We move from eleven (sixty-nine, really) terrified individuals--almost all of them fled like scared rabbits when their Messiah was captured by Roman guards--to just as many fearless martyrs three days later. My question to those who doubt the accounts of the gospel would be this: from whence cometh this boldness? The fact that they all attested to Christ's resurrection (which was the proof He said He'd give for all the other claims' validity) with their very lives at stake says to me that the gospel accounts--most importantly, the claims of Christ therein concerning Himself--are at best trustworthy as to what was said by Christ, even if the veracity of said claims is still up for debate.[/
I don't think I have any answers that would persuade a Christian. I'm not even sure that I have answers that I would find persuasive, lol. Was it group delusion, caused by the trauma that they were surely experiencing? Possible, but very unlikely. Was it just a case of misremembering? I can see the not remembering this saying or that action, but I don't think they could forget something like a guy rising or not rising from the dead. Perhaps they just realised that Jesus never meant to reestablish an earthly kingdom, and since their beliefs were incorrect, they decided to reinterpret the ministry of Jesus in a wholly new way? Perhaps the resurrection stories were intended as myths for inspiring Christians to devote themselves to God and trust in him for their salvation? As you yourself said, when someone believes that something is true, they will go even as far as martyrdom to support the truth. While it's not as likely in the Christian case, there have probably been people who died for things that they knew were myths, because they believed in the ideas within those myths (also, Christians were not put to death for believing that Jesus was resurrected, but for other reasons). There are probably other possibilities that I'm not thinking of.
Also, I think the teachings in the text itself are such that I couldn't accept them. There are ones that many people struggle with, like the concept of an eternal hell. There are other issues, though, such as my belief that the prophecy of Jesus that "the gates of hades will not prevail against you" has failed. That, combined with the doubts mentioned above, and some others, leads me to where I am.