1) God is the greatest conceivable Being/Thing.
2) In order for God to be the greatest conceivable Being/Thing He must exist not only as a concept but also in reality. Otherwise, something greater can be thought of (a being/thing that exists in concept and reality).
3) Nothing Greater can be thought of than God (A being/thing that is all knowing, all powerful, and present in all places).

Conclusion: God exists in reality

1) God is the greatest conceivable Being/Thing.
2) In order for God to be the greatest conceivable Being/Thing He must exist not only as a concept but also in reality. Otherwise, something greater can be thought of (a being/thing that exists in concept and reality).
3) Nothing Greater can be thought of than God (A being/thing that is all knowing, all powerful, and present in all places).

Conclusion: God exists in reality

I think your argument asserts that a reasonable belief in God must be integrated with the material world and reason or else it is just imagination.  I think roman catholicism accomplished that goal, but then the reformation tried to undo that (most clearly illustrated in the catholic belief in transubstantiation and the protestant denial of it).  And, if i understand it correctly, out of that came things like the enlightenment idea of man as a machine or german idealism versus german materialism.  Also, Jєωs are supposed to have gone through something of their own, in the 17th century, when their "messiah" converted to islam rather than face execution and so their culture split, into one side taking reason and the other taking faith and the two having little to do with each other.  

I would restate your conclusion as:  God exists in reality or does not exist.  

Ah, yes. St.Anselm's now famous ontological argument. It has its defenders (although typically reformulated more formally using modal logic) even today, but after St.Thomas, many Catholic philosophers did not employ it.

Yeah I think its a variation of Anselm's argument. I found it just roaming around on the internet one day. I think this was reformulated by a student at a university somewhere. I can't see any flaw in it.

Saint Thomas Aquinas rejected this proof. He argued that the human mind cannot conceive of a being such as God. He held to a negative theology, in which we can only understand God by deducing what he is not. For instance, God cannot be composed of matter, for that would mean that God could be moved, but God as an all powerful being cannot be moved. We have no means of comprehending God, and so the argument cannot be used to prove his existence. Better to just stick with the Five Ways, or something similar.

Yes, I'd say unbelievers are typically more unlikely to be swayed by the ontological argument than say, by the cosmological or teleological argument. The Catholic Church teaches based on sacred Scripture that God "can be known with certainty from the consideration of created things, by the natural power of human reason : ever since the creation of the world, his invisible nature has been clearly perceived in the things that have been made" again, as the Angelic Doctor had said, as a cause is known from its effects. I agree with Lybus that the Five Ways may be more powerful in this regard.

On the contrary, It is said in the person of God: "I am Who am." (Exodus 3:14)

I answer that, The existence of God can be proved in five ways.

The first and more manifest way is the argument from motion. It is certain, and evident to our senses, that in the world some things are in motion. Now whatever is in motion is put in motion by another, for nothing can be in motion except it is in potentiality to that towards which it is in motion; whereas a thing moves inasmuch as it is in act. For motion is nothing else than the reduction of something from potentiality to actuality. But nothing can be reduced from potentiality to actuality, except by something in a state of actuality. Thus that which is actually hot, as fire, makes wood, which is potentially hot, to be actually hot, and thereby moves and changes it. Now it is not possible that the same thing should be at once in actuality and potentiality in the same respect, but only in different respects. For what is actually hot cannot simultaneously be potentially hot; but it is simultaneously potentially cold. It is therefore impossible that in the same respect and in the same way a thing should be both mover and moved, i.e. that it should move itself. Therefore, whatever is in motion must be put in motion by another. If that by which it is put in motion be itself put in motion, then this also must needs be put in motion by another, and that by another again. But this cannot go on to infinity, because then there would be no first mover, and, consequently, no other mover; seeing that subsequent movers move only inasmuch as they are put in motion by the first mover; as the staff moves only because it is put in motion by the hand. Therefore it is necessary to arrive at a first mover, put in motion by no other; and this everyone understands to be God.

The second way is from the nature of the efficient cause. In the world of sense we find there is an order of efficient causes. There is no case known (neither is it, indeed, possible) in which a thing is found to be the efficient cause of itself; for so it would be prior to itself, which is impossible. Now in efficient causes it is not possible to go on to infinity, because in all efficient causes following in order, the first is the cause of the intermediate cause, and the intermediate is the cause of the ultimate cause, whether the intermediate cause be several, or only one. Now to take away the cause is to take away the effect. Therefore, if there be no first cause among efficient causes, there will be no ultimate, nor any intermediate cause. But if in efficient causes it is possible to go on to infinity, there will be no first efficient cause, neither will there be an ultimate effect, nor any intermediate efficient causes; all of which is plainly false. Therefore it is necessary to admit a first efficient cause, to which everyone gives the name of God.

The third way is taken from possibility and necessity, and runs thus. We find in nature things that are possible to be and not to be, since they are found to be generated, and to corrupt, and consequently, they are possible to be and not to be. But it is impossible for these always to exist, for that which is possible not to be at some time is not. Therefore, if everything is possible not to be, then at one time there could have been nothing in existence. Now if this were true, even now there would be nothing in existence, because that which does not exist only begins to exist by something already existing. Therefore, if at one time nothing was in existence, it would have been impossible for anything to have begun to exist; and thus even now nothing would be in existence — which is absurd. Therefore, not all beings are merely possible, but there must exist something the existence of which is necessary. But every necessary thing either has its necessity caused by another, or not. Now it is impossible to go on to infinity in necessary things which have their necessity caused by another, as has been already proved in regard to efficient causes. Therefore we cannot but postulate the existence of some being having of itself its own necessity, and not receiving it from another, but rather causing in others their necessity. This all men speak of as God.

The fourth way is taken from the gradation to be found in things. Among beings there are some more and some less good, true, noble and the like. But "more" and "less" are predicated of different things, according as they resemble in their different ways something which is the maximum, as a thing is said to be hotter according as it more nearly resembles that which is hottest; so that there is something which is truest, something best, something noblest and, consequently, something which is uttermost being; for those things that are greatest in truth are greatest in being, as it is written in Metaph. ii. Now the maximum in any genus is the cause of all in that genus; as fire, which is the maximum heat, is the cause of all hot things. Therefore there must also be something which is to all beings the cause of their being, goodness, and every other perfection; and this we call God.

The fifth way is taken from the governance of the world. We see that things which lack intelligence, such as natural bodies, act for an end, and this is evident from their acting always, or nearly always, in the same way, so as to obtain the best result. Hence it is plain that not fortuitously, but designedly, do they achieve their end. Now whatever lacks intelligence cannot move towards an end, unless it be directed by some being endowed with knowledge and intelligence; as the arrow is shot to its mark by the archer. Therefore some intelligent being exists by whom all natural things are directed to their end; and this being we call God.