These have all been refuted in one way or another, but they're still pretty badass. Which one's your fave?
Anselm
Anselm of Canterbury was an insanely devious motherfucker who chilled out in the 11th century. His proof of God was so badass that no one could figure out a good answer to it for hundreds of years.
Here's how he would get you with it:
Anselm: Oh, hey there Mr. Atheist - quick question for you - do you accept that if there is a God that our understanding of Him is as a being who is so fucking awesome that it would be impossible to imagine something more awesome?
You: Sure, OK whatever, but I still don't think that being actually exists.
Anselm: Yeah, but your idea of it exists in your mind, doesn't it?
You: Yeeeeeeah, so what?
Anselm: Well, I was just thinking that something that exists in reality is even better than some dumb thing that only exists in your mind. Right?
You: Duh, yes, obvs. Where are you going with this, Anselm?
Anselm: Where I am going with this is that if God exists in your mind, which you ALREADY ADMITTED THAT HE DOES, then we can imagine something that's even better than that - a God that exists in reality.
You: And?
Anselm: Remember how we started off by agreeing that we can't imagine something better than God?
You: Uh-oh.
Anselm: Yeah. You just got owned. QED, bitch.
Aquinas
Thomas Aquinas was so good at proving God that he did it five times. He would essentially just sit around taking massive bong rips* and coming up with proofs of God that totally blew everyone's miiiiiiiinds.
Like, for instance, he would be all:
1. Yo, have you ever you noticed that the hotter something gets, the closer it gets to being, like, the hottest thing in the world?
2. And don't you think that's kind of true of, like, everything? Like, the more intense that something gets, the closer it gets to being, like, the most totally intense version of that thing?
3. But anyway, so that made me think that there's gotta be something that has all the properties to the max. You know? And then I was like, oh, shit, I just proved God again.
*Probably not.
Aquinas, Back For Round 2
When Aquinas wasn't high as a fucking kite on the finest Humboldt county weed, he liked to sit around adapting some Ancient Greek knowledge bombs into airtight proofs of his number one dude, the big man in the sky. One of his chart-topping hits in this genre was the Cosmological Argument, and it went a little bit like this:
1. True fact: Everything that isn't infinite has a cause.
2. True fact numero dos: None of those things can cause themselves, because that would be stupid.
3. One more true-ass fact for y'all, just 'cuz I'm feeling generous: A causal chain can't be of infinite length.
4. Where does that leave us? Glad you asked. It leaves us with some irrefutable-ass knowledge that there has to be a first cause of everything. This may surprise you, but I'm going to go ahead and call that first cause G to the O to the motherfucking D. Boom.
Kant
Immanuel Kant's whole thing was that he would go around critiquing everything like he was so much better than the rest of us, but when he wasn't nitpicking and being a back-seat driver, he could occasionally make himself pretty useful in the God-proving department.
In his Critique of Practical Reason, which is essentially just him shitting all over practical reason just because he felt like it, he took a little time out to prove everybody's favorite deity using a little old thing called the Moral Argument. It went like this:
1. You know what's awesome? It's awesome when people are both morally virtuous and happy. Actually, that is so awesome that it is literally the most awesome thing that can happen.
2. You know what else I've noticed? Pretty much everybody who's not, like, totally nuts feels rationally compelled to try and be good and happy in their lives.
3. And you can't be compelled by reason to do something that's impossible, is all I'm saying.
4. Yeah, and just one more thing: If there is no God or afterlife, it's not possible to attain the highest good. Which means that there are those things. BOOM.