Byrne covers: Phoenix Untold Story 1 and Fantastic Four 247.

Non-Byrne Superhero: Sheild 6, Green Lantern 76, Hulk Annual 1, Tales to Astonish 93, Detective 475 and the Neal Adams Batman/Detective??? cover where Robin is turning to dust in an anquished Batman's arms.  Can't remember the issue number to that one. Last but not least Animal Man 24 by the brilliant Brian Bolland.

Golden age: pretty much anything by Schomburg or Raboy, but especially All Select 2.

Golden Age Horror: Black Cat Mystery 50 and Suspense Comics 3

My first FF and still one of my favorite coverrs.

Are symbolic covers such as this FF example more prevalent in DC than in Marvel?

Just to add, that cover you posted was not strictly speaking a symbolic one, even though IIRC the story was inspired by a few Giant Doom symbolic covers like this one...

And following that issue, the one I still find the most disturbing of all...

To this day I wonder why Mr. Fantastic would be so far out of character.

My current obsession:

:

Miller had an incredible run of iconic covers.

Here's another (can't seem to attach multiple images in one post ..)

One more

You know, this one could be the greatest of all time (if you think about it)...