Honestly Gaimens series while good in itself did pretty much retconed everything else that had come before in regards to the Eternals. It is best to just read it on its own after you have read the more classic stuff. I really did not care for most of the Eternals stuff after the Gaimen mini series that much either since to me it seemed to lose what made them special to begin with.
I would say look for:
Eternals vol 1 (19 issues by Kirby)
Thor: The Eternals Saga (Thor issues 283-301 Annual 7)
Eternals vol 2 (12 issues maxi series)
Avengers (issues 246-248)
Iron Man Annual #6
Silver Surfer Annual #1