Most office copiers will duplex these days. They often have a lot of other fancy features too. At work they have an old one, but it has a NIC so you can print to it on the network, it will collate and staple, has a bunch of different drawers for various types of paper, has FAX built-in, and it's color.
They still use the same business model of renting or leasing you the copier though. You can buy them outright, but from what I've seen most places don't do that, they just call up the local "Foobar Business Machines" and have them roll in a copier and then maintain it.
I've been to a couple of places that still use mainframes and have print shops for printing from the mainframe. They had some pretty impressive-looking equipment, although I really don't know that much about them. I just know they do high speed and high volume printing, and that reliability is very important.
A friend has talked about the printing equipment they have in the radiology dept at a local hospital where he works. It sounded like it was pretty massive too, and very expensive. :)