Some of these are easy:
Superman::Lex Luthor
Fantastic Four::Dr. Doom
Batman::The Joker
X-Men::Magneto
But for other heroes it’s not as clear-cut. Is Spider-Man’s opposite number Doctor Octopus or the Green Goblin (my inspiration for this thread was learning that it’s Green Goblin in the movie, not Doc Ock)?
Is Green Lantern’s Sinestro, or Star Sapphire?
Who is the Flash’s, or the Incredible Hulk’s?
Did the Lone Ranger have one?
Let’s get to work.
Could you just take the easy way out and say “Themselves”? I mean, it seems every character has a storyline where they have to fight an evil version of themselves, and who can be worse for you to fight than you on a bad hair day?
Not sure who Spiderman’s arch-nemesis would be. Green Goblin seems the most likely choice.
You gotta give Sinestro the status of Green Lantern’s arch-enemy, since they both have a power ring.
Flash’s arch-nemesis is difficult to pin down. My first guess would be the Reverse-Flash (if we’re talking about Barry Allen). But I really consider Flash to be against the entire Rogues Gallery (Capt. Cold, Mirror Master, Capt. Boomerang, etc.).
No idea for Incredible Hulk or Lone Ranger.
Here are some more:
Captain Marvel : Dr. Sivana
Starman : The Mist
Captain America : Red Skull
Aquaman : Black Manta?
Wonder Woman: Cheetah? Ares? Circe? Giganta?
I’ll try to think of some more…
Well, for the Hulk, I’d have to pick The Leader. There’s a nice brains vs. brawn split.
Yes on Sinestro for Green Lantern.
Wonder Woman: Cheetah.
I’ll be back with more.
Underdog - Simon Bar Sinister
Honey
silver surfer vs. galactus
wolverine vs. sabretooth
thor vs. loki
daredevil vs. kingpin
dr. strange and dormammu
silver surfer vs. galactus
wolverine vs. sabretooth
thor vs. loki
daredevil vs. kingpin
dr. strange vs. dormammu
I’d say one of the strengths of the Spider-Man franchise is that there hasn’t just been one. The many writers over the years have been able to weave a convincing number of nemeseseses into the overall story of our friendly neighborhood Spider-Man without relying on “Okay, we’re out of ideas – let’s just bring in the Green Goblin, 'cause he’s Spidey’s arch-nemesis.”
I’d pick the Maestro for the Hulk. Yes, it is an evil dupe, but an OLD evil dupe…
Martian Manhunter: A poorly tended campfire? Actually I don’t think he has one…
For Spider-man: I’d have to disagree again, I’d pick Venom. Or would that fall under the Evil Duplicate part again?
Thor: Lokii wouldn’t put down venom for spiderman. venom’s pretty new on the scene. i’d say j jonah jamison. not exactly a supervillain, but he’s the one guy peter parker could never get rid of.
Jameson is Peter Parker’s arch-nemesis, not Spider-Man’s.
David Banner/Hulk v McGee ( on tv anyway)
I’d have to agree that Venom is Spidey’s arch nemesis, simply because Venom’s whole purpose for being is to kill Spider-Man. Everyone else wants to take over the world and take Spidey out as a bonus, but Venom has no other motives, and that makes him even more dangerous. Plus, he knows all of Spidey’s secrets.
As for the Hulk, I’d go back to my original post in a sense and say his nemesis is Bruce Banner. Of all people the Hulk hates the most, Banner tops the list, and vice versa. The Leader would be my second pick, but he just blew up, so I guess he no longer counts.
The Punisher=Jigsaw
most of the comics I read now have been chosen or have no real villains. The Authority just seem to piss off everybody.
The Warlord’s was Deimos. He had to kill that guy … 3 or 4 times. And then he had to kill his ancestor from 5,000 years in the past who looked just like him. He was a real bastard too.
Underdog’s archnemesis was Simon Barsinister. Simon says … die!
Spawn - Malebolgia (or whatever the hell his name is)
christ i had some others but i forgots
Captain America - Red Skull
Cyclops - Mr Sinsiter
Batman - Blight (if we’re talking Terry McGinnis/Batman in Batman Beyond…)
Johnny Cash - Barry Manilow
Anyone know if Hawkman or Dr Fate have arch-enemies?
Wasn’t the Lone Ranger’s enemy Butch Cavendish, or something like that?
I’d have to agree that Jonah Jameson is (or at least was, I haven’t read a Spidey comic since the 80’s) Spiderman’s arch-nemesis. He wasn’t Parker’s nemesis, he was his employer! Many of Spidey’s villians came from Jonah in one way or another, or at least gave him more trouble because of Jonah. The Green Goblin (and all the subsequent goblins who came after) is a good choice too, though.
For the same reasons, only more so, I’d have to say Thunderbolt Ross is the Hulk’s arch-nemesis.
Savage Dragon=Overlord (is that right? The guy in the suit)
Batman=the Joker (he’s got so damn many, but this is the one that seems to get under his skin the most)
Bart Simpson – Sideshow Bob and Dr. Demento
Tom Terrific – Crabby Appleton (“Rotten to the Core”)
Beany and Cecil – Dishonest John
Dudley Do-Right – Snidely Whiplash
Rocky & Bullwinkle – Boris & Natasha
The Black Spy – The White Spy (and the Gray Spy for them both)
Bugs Bunny – Elmer Fudd
Flash – Super Gorilla Grodd, of course.
The Heckler – Bushwack’r 
The Cavendish Mob killed the Lone Ranger’s brother, but they were displosed of pretty quickly.