Moore's Swamp Thing (most of which took place pre-COIE) is probably my favorite pre-Crisis run.
Others:
Wolfman/Perez on NTT- melodramatic and dated, but still the best ensemble writing the title has seen, and the stretch from the first Blackfire arc until Perez's first departure hold up better than the rest of it.
Levitz on Legion of Superheroes
Alan Moore's Superman stories
Kirby's Fourth World stuff
Englehart/Rogers on Detective Comics.