Zed for the Champions you could go.
1) Hercules (He could be added to quite a few groups really)
2) Angel (again, oh well at least he wont be blue)
3) Darkstar (seeing she hasn't been made yet)
Good call on Darkstar, been so long since I read the Champions I had forgotten about her completely being on the team.
Still my primary's are Angel (as angel, not that I mind archangel too, but again that founding member idea) and Herc for the founders of the team are my primary thought.
Something else I thought of too was the remaining 4 horsemen of Apocalypse, I don't see hasbro doing it as none of the characters are really recognizeable, but would be cool anyway.