[Life and Death of Superman] - that's some classic Superman right there. Superman vs Doomsday is literally my favorite fight in comics that I've ever read. It would be wise to not forget [Red Son] which like TDKR tells a what if story, of what if Superman landed in Russia instead of USA. Maybe you'll have better luck than I did in finding [Superman: Blue] I can find evidence it exists it wasn't just a dream I had but I can't find evidence that it's anywhere. To be fair most people seem to dislike it based on the less than 7 reviews I've read but I read the back of the graphic novel and I was intrigued. The idea is that Superman doesn't have his powers and develops new ones. Instead of stopping bullets, They phase right through him. He's still invulnerable but it's harder to protect people when you can't be a body shield anymore....etc etc etc.
[Knightfall] - a fantastic Batman book that introduced someone more powerful than batman. There's [The Killing Joke] which if I have my stories correct is how Batgirl got paralyzed (sorry for the spoiler but there's a lot of good beyond that)
If you're familiar with Batman already then you can't go wrong with [The Dark Knight Returns] there's a reason it's so revered. Again not the typical Batman story but it's awesome.
Static/Static Shock - because that is some freaking hard junk to find. At this point I would literally pay for Static but I can only find the first run of Static first fun of Static Shock and first fun of new 52 Static. Those are the only ones grouped into graphic novels that I can tell. It's only made me hungry for more.
These are kinda the stories of my youth with the exception of Static that I wish I'd known about back then.
I know it's not golden age but I don't read much marvel in part because I'm still stupidly loyal to DC, in part because I have less interest in their characters and in part because I haven't read much comic books lately, but I would greatly recommend [Planet Hulk --> World War Hulk]. It's a fantastic story in one of the few Marvel characters I like. Planet Hulk literally brings a tear to my eye every time I read it. I heard it hugely recommended at the time and eventually I broke down and read it. Best decision ever.
[Identity Crisis] is a cool JLA story. If you've seen Teen Titans the show that'll help just a skosh. But it's a mystery and it's certainly an interesting one. It's been somewhat controversial in the comic book scene for reasons I can't reveal but should be fairly obvious in the end. But it has a lot of great comic elements.