This is the second thread I've run into that's attempting to list Marvel VS DC counterparts. The original motive seems to have been simple "most evenly matched for an X VS Y" movie, but keep in mind that marvel and DC used to rip each other off constantly, and as such, many characters have exact counterparts to each other in the opposite universe.
Sorry for being so wordy, but I've been looking for such a list recently, and since I can't find one I was hoping we could make one.
Etrigan – the Son of Satan
Dr. Strange – Dr. Fate
Swamp Thing – Man Thing
Elongated Man / Plastic Man – Mr. Fantastic
Killer Frost - Ice Man
And just for the record ...
Batman - Iron Man
Those two are essentially each others equivalents: The millionaire playboy with no real superhuman powers who basically gets to play superhero due to infinite funding.
If somebody wants to argue that Batman wouldn't stand a chance against Ironman's suit, please keep in mind that on several occasions Batman has worn a special armored "Iron Man" like version of his bat costume.