I enjoyed looking at this Comics Should Be Good post on triptych covers (although it quickly expands beyond that). He’s collected a whole bunch of comic images where two or more covers put together make one big picture.

Several I remembered, but many were new to me, and I had no idea some now-defunct companies had done as many as eight! (Bigger’s not always better, gang.) Some simply stick in a common background behind generic individual hero shots, but the coolest ones, like Kid Eternity or especially Starman, add up to something more.