For those of you that don't know, atheism is the lack of belief in gods. I am an atheist. This position is sometimes clarified as "weak atheism" to differentiate it from "strong atheism". "Strong atheism" is the belief that there are no gods. Take a moment if you need it to see the difference between those two statements.
Now take a journey with me on a different (but converging) train of thought. I believe in the existence of tables (a flat surface, held off the floor often by means of four vertical legs). I really do. When I see a table, I include its existence in my set of relevant sensory data. When I need to set something down, I often choose to use a table, and they never let me down by not existing. You might say I am a "tableist".
Santa Claus, on the other hand, is something in which I do not believe. I even take it a step further. I actively disbelieve in Santa. Because not only do I have no evidence of his existence, his existence actually contradicts many things that I know about the world in which I live. In order for Santa to exist, many of the laws of physics need to be able to take temporary vacations on Christmas. Additionally, there needs to be a huge conspiracy. If you're a parent (like me), you know where the presents come from. So in order for Santa to be real, you have to be willing to believe that your memory has been altered every year, with false memories planted by Santa's elves. This is all ludicrous, and so I would describe myself as a "strong aSantaist"*. Note: That's aSantaist, not Satanist.
Here is where the trains converge. When it comes to Christianity, the god that it claims exists is similarly problematic. In order for it exist, many of the laws of physics are just guidelines. Additionally, there is a huge conspiracy in which prayers are being answered all the time, but always in such a way that they can never be detected using science and statistics. This god is either intensely camera-shy or nonexistent. When speaking of the god of Christianity, I am a "strong atheist".
Humorously enough, I am a "strong atheist" for most of the gods that people posit. There are too many logical problems with any sort of omnipotent, omniscient, omnibenevolent, yet-somehow-still-personal god that most people believe in.
This leaves only a couple of leftover possibilities. One is the deist's god. The deist's god is usually described in such a way as to be virtually indetectible. He exists outside the universe and doesn't interfere in it. He also is not a person in any way that we would recognize. I can't be a "strong atheist" on this one, because it doesn't contradict any observations about the world in which I live. I am willing to posit that something like that might exist. But since I don't have (and never could have) any evidence for it, my position is "weak atheism". If it turned out it did exist, so what? In what way would the universe where such a god does exist differ from one in which he does not.
The other possibility is the pantheist's god. The pantheist's god is the universe. Everything that exists somehow makes up a being that created itself. Like the deist's god, it is not a person. And once again, no evidence for this idea, so "weak atheism" is my response. And once again, so what if it were true? What would (or could) you do differently if you were one of the miniscule unknowing components of a universe-god-being? In fact, it seems like a silly way to change the name of the universe from "universe" to "god".
So I guess what I'm saying is that generally, I'd have to admit to being a "weak atheist". I've seen no evidence for any supernatural beings, but there are some that wouldn't leave any evidence, so I just don't believe in those. As for those that contradict the evidence, I'm a "strong atheist" all the way.
* Please keep in mind that "strong aSantaist" does not mean dogmatic aSantaist. I'd be perfectly willing to start believing in Santa once I get that evidence. Only sadly, since Santa contradicts what we know of physics as well as our own personal observations, it's going to take a load of evidence to be convincing. Seeing Santa in a dream, not good enough. Speaking to Santa in person, I've probably gone crazy. Having Santa appear to everyone in the world at once (displaying his awesome powers), now we're talking. At that point, I for one would be welcoming our new elvish overlords.