Judge Dredd: The Cursed Earth

Start here, with Case Files 01 beforehand if you want the first year of one-offs. Dredd drives a vaccine across the nuclear wasteland to plague-hit Mega-City Two, and the journey sketches most of what lies beyond the city walls. Written largely by Pat Mills, it was the first Dredd story to run past twenty episodes. Case Files 02 reprints it without parts 11, 12, 17 and 18, so expect a couple of jumps.