Two of the longer running ending titles were the Flash and World's Finest Comics.
Each were there for the beginnings of DC's Silver Age, but had run their course....
World's Finest Comicsteaming up with Superman #76 (May-June, 1952), but began regular team-ups with World's Finest Comics #71 (July-August, 1954), with these issues being some of the earliest tales of what would be called Earth-1, with the friendship of Superman and Batman being a foundation of that world, even before the existence of the Justice League of America, or the existence of a hero which started the Silver Age.
the Outsiders, and though they patched things up, the title came to an end with World's Finest Comics #323 (January, 1986) as the Crisis On Infinite Earths was on its 10th issue.
The FlashGolden Age Flash with Flash #105 (February-March, 1959), soon after helping to form the Justice League of America along with Superman and Batman (and a few others), and even having a hand in finding the multiple Earths with the Golden Age Flash.
Suicide Squad), picked up his own title, Flash #1 (June, 1987)...proving "every new beginning comes from some other beginning's end"!