Most Apple printers will work with the 128K as long as it's supported by System 2.0/Finder 4.1. The LaserWriter 7 driver from System 6.0.8 is compatible all the way back, so there's a benchmark by which to guess which printers should work. Most were not serial protocol, per se, but rather AppleTalk networking over the serial port, which is why the 128K is so forward compatible. However, if you're running pre-System 2.0/4.1, you'll be limited to the ImageWriter, I believe.

You can also print to a postscript file using the LaserWriter 7 driver and print it on a modern Mac.