The Story: "No More Tomorrows!" by Mike Friedrich, Dick Dillin, and Joe Giella. Sargon the Sorcerer shows up in the JLA Satellite, and informs them(after he holds off an attack by them, classic Marvel misunderstanding style) that the Starbreaker can defeat any physical attack by them, they need the assistance of magic!
He says they need two other magical talismans to go along with his Ruby of Life, and dispatches the JLA to retrieve them. Aquaman and Black Canary are sent to Sierra Verde, where they obtain the mystic ruby--but only due to the use of their very specific powers. Almost as if Sargon knew...
The same thing happens with Batman and Hawkman, and they all reconnoiter at the satellite, where Sargon enlists them all in a seance. He tells them "Within these mystic gems surgers the only force mankind can use to overcome its death-fears--love-power!" And this guy's a master sorcerer?
Anyway, he links up the power from GL's ring, the Hawks' futuristic weaponry, and the "myriad of alien power-banks " in Superman's Fortress of Solitude, featuring cameos by Hawkgirl and Supergirl. Hawkgirl is ok, but who the heck drew that Supergirl panel?:
Anyway, the JLA, with the addition of these magical energies, defeat Starbreaker(with the specific help of the Atom) and bring him back to the satellite. It's here that Sargon strips the cosmic vampire of all his destructive power, and the Guardians of Oa take possession of the unconscious Starbreaker.
Roll Call: Superman, Batman, Aquaman, Flash, Green Lantern, Green Arrow, Atom, Hawkman, Black Canary
Notable Moments: This was a real Sargon-centric(and when has that phrase ever been used before?) issue--not only does he guest-star and basically save the JLA's bacon, but this issue reprints a solo Sargon story from Sensation Comics #70. There's also a Starman story from Adventure Comics.
I'm not sure how Thanagarian futuristic weaponry helps with magic, but I supposed Sargon knows his business.
Shameless Plug Department: Frequent commenter and regular contributor to the Rob Kelly Family of Blogs Vincent Bartilucci has a great story about this very issue of JLA over at Hey Kids! Comics!, go check it out!