Captain Marvel (Billy)
Captain/Mary Marvel
CM3
Black Adam
Thunder (from the Legion of Super-Heroes)

AND...........

Gwen Stacy
Captain Stacy
Supergirl (Pre-Crisis)
Flash (Barry Allen)
Captain Mar-Vell
Thunderbird
The Hellions
Most of the Morlocks during the Marauder Raids
Colossus
Illyana Rasputin (Majik)
Nova
Air Walker
Moira MacTaggart
Destiny
Pyro
Betsy Ross/Banner
Guardian (I think)

There are a few more but my mind hurts from trying to do this and look busy at work.

yep Rogue2, Thunder was the harder one to get the other 4 were quite simple

In John Stewart's first adventure with the JLA (when they squared off against the Key over the Christmas Holidays), why was he acting as Green Lantern and not Hal Jordan?

Hal slipped on a bar of soap.

Correct. The first story I ever read with John Stewart. I thought he was awesome. But I found it strange that the ring didn't get help for Hal, or let the others know what was happening. Of course, I was 6 or 7 and can't really remember a lot of the rest of the story.

Your question I_M

OK, so new question, from the same era:

What was the name of Galactus-esque planet-eating "Space Vampire" that the JLA fought?

wasn't it Yuba Kahn?

Nope.

Oh, wait... That's Darkseid's father. Was it Manga Kahn?

Nope, Manga Khan (a pun, substitute "comic" for manga and you get Comic Con) is far, far later than what I'm thinking of.

IT WAS STAR SOMETHING

Was it Starro?

Perhaps is is too lame for anyone to remember. He was indeed quite lame for a character who was supposed to be so menacing.

It was StarBreaker.

New question: Why is the town "Four Heroes, Maine" named that?

Wasn't that when the original Doom Patrol sacrificed themselves to save the town? It appeared everyone died except Robotman (Cliff Steele).