I drive around NYC a lot, and it is an absolute bone jarring ride.

I can't even imagine doing it on 18" rims.
Too much PSI will blow your tires, but too little PSI will dent your rims. You have to find a good setting in between.
The other word of advice (which is equally difficult in NYC) is to slow down. By slowing down you reduce the force that you hit the potholes with, which will help protect your tires and rims.
That said, there is only so much you can do. I was going up 8th Ave yesterday around the Port Authority, and it felt like all 4 wheels were going to be trashed. And that was taking it slow!