In Watchmen, Dr. Manhattan acts as the Foil to both Rorschach and Ozymandias. Watchmen is full of these. Rorschach and Ozymandias are very obviously foils, since their lifestyles, methods and ideologies are the exact opposite (Rorschach is a deontologist while Ozymandias is consequentialist, Rorschach is ugly while Ozymandias is handsome, Rorschach lives in squalor while Ozymandias is rich, Rorschach is Asexual while Ozymandias might be homosexual, etc). Another obvious pair is Nite Owl II and Manhattan, enhanced by Laurie having had a relationship with both of them (Dan is receptive while Jon is distant, Dan is out of shape and middle-aged while Jon is in perfect shape and eternally thirty, etc)
Superman and Brainiac as well. The former is an alien who has allowed himself to become fully human. The latter is the very cold, remote, and incredibly dangerous alien that people like Luthor expect Superman to be.
Superman and General Zod as well. Superman is the ultimate immigrant, bringing the best of his homeland to his new world, and standing for the peaceful synthesis of culture through understanding. Zod is the reason why people fled the Old Country in the first place, and when he travels, it's only to head an invasion force.
Superman and Darkseid. Superman representing the idea that people are basically good, Darkseid believing that people cannot be trusted with their own free will. In short, Hope Bringer versus Hope Crusher.
For a more allied/friendly flavor, Batman and Superman are often this to each other in terms of Brains and Brawn, respectively.
Supergirl and Lobo in the Red Daughter of Krypton storyline. Says writer Tony Bedard: "Lobo is there as a sort of dark reflection of her. They're both super-powerful loners left over from dead planets. Lobo has channeled his power and rage into becoming the most dangerous bounty-hunter/assassin in the galaxy. Supergirl's still trying to figure out what to do with her power and her lot in life. Tangling with Lobo will show her one path she might go down. It's really a cautionary tale for her, and she'll come away knowing that she could easily end up like him if she doesn't get her act together."
X-Men and all anti-mutant organizations. Charles Xavier and Magneto, as well. Former friends with similar goals (acceptance for mutants), but vastly different philosophies and methodologies (helping humanity and proving their worth in the process vs. warring against humanity and overthrowing or exterminating them).
Spider-Man and Green Goblin, where the foil occurs in their completely different characters and social status.
Also applies to Spider-Man and Doctor Octopus after Octavius spent some time acting as the 'superior Spider-Man' while in Peter Parker's body, as Octavius finally chose to sacrifice his existence to restore Peter when he accepted that he bragged about his own superiority to conceal hi awareness of his own flaws while Peter accepted his responsibility quietly to take on what burdens he could.
Rounding out the trio of Spidey's big three villains is Venom. They bear the same power set, even through similar circumstances, but they have different upbringings: Peter was raised by his aunt and uncle after his parents' deaths, while Eddie only had his father to try and earn even basic respect from. Both fight criminals as well, though while Spider-Man believes in Comes Great Responsibility and holds a Thou Shalt Not Kill code, Venom blatantly ignores said responsibilities and prides in lethal force, killing even basic muggers in a delusional belief in justice. Lastly, Spider-Man is vividly colored, with Venom being Deliberately Monochrome.
Iron Man and Mandarin: Being opposites on the Tech vs Magic scale. Additionally, where Tony is the ultimate futurist and is firmly ensconced within capitalism, The Mandarin is a feudalist who longs for a return to the past.
The The Incredible Hulk and The Leader, as raw strength contrasting with enhanced intelligence. Also Hulk and Thunderbolt Ross.
In Hellblazer, John Constantine has his best mate and sidekick Chas Chandler as an example. Both these two are good friends, but often different in many ways. John is cynical, while Chas is an optimist. John is a lazy bum who is addicted to adventure, while Chas is a hardworking taxi driver who wants nothing more than to keep himself in one piece. But these two are inseparable even in the hardest times of their friendship.
In Jeremiah, by Hermann: The protagonist's partner, Kurdy Malloy, is much more cynical, streetwise and childish than he is. Jeremiah is no fool by any means, and he is an action guy, but he is much nobler and more romantic than his friend, and puts more trust in others.
Corto Maltese, by Hugo Pratt: he does not have a permanent "sidekick", but many times he has adventure partners who are much crazier and more violent than him: Rasputin, an Ethiopian warrior, A Chinese Assassin girl. He also has had partners who are more of the "professor" type, which turns him into the guy who leads the action.
Astro City features The Cape, Samaritan, and his arch-enemy the Infidel. Samaritan comes from the distant future (having come back in time to avert a Bad Future), sees the good in everyone around him. Infidel comes from the distant past, sees everyone as small-minded and ignorant. Samaritan is a strict minimalist in the use of his powers, while Infidel uses them for every single task he's faced with. Both use Appropriated Appellation — Samaritan made his debut saving lives, while Infidel got his name from deliberately breaking every taboo he can think of.
Wolverine and Cyclops have always had a relationship like this, though it goes deeper than it might appear at first glance. Wolverine is a scruffy loner who wears his rage on his sleeve, Cyclops is a clean-cut leader known for his stoic personality and his deeply repressed self-doubt; Wolverine is a skilled hand-to-hand brawler with brute strength on his side, Cyclops is a cold strategist with a long-range laser cannon built into his eyes; Wolverine is a veteran soldier and former mercenary who was Walking the Earth for years before he met the X-Men, Cyclops grew up at the Xavier Institute through his awkward adolescent years; Wolverine remains aloof from the team, Cyclops sees them as his only true family; Wolverine turns out to have a surprisingly idealistic heart under his gruff exterior, Cyclops turns out to be surprisingly manipulative and calculating under his respectable exterior.
Reed Richards and Victor Van Damme from Ultimate Fantastic Four both share a similar backstory, suffering at the hands of abusive fathers, pouring all their energy into science at a young age. Unlike Victor, however, Reed had a loving mother and younger sister, as well as a best friend in the form of Ben Grimm, which kept his life from being a living hell. Ultimate Mystery and Ultimate Doom shows us that even a loving mother, sister and best friend isn't enough to keep Reed from going over the deep end to the point where the heroes are wondering if he's just Doom II.
They were the two primary teenage teams of Marvel in the '00s. Outside the fact that they're both powered crimefighters in the teenage range filled with a wide assortment of power types and origins, they contrast each other greatly. The Runaways did not jump at the call, they were shoved, on the other hand, the Young Avengers all became superheroes with the full intent and desire to be. Runaways eschew many of the tropes associated with the genre, as in they don't have costumes or codenames (their attempts to adopt them fell flat). In contrast, the Young Avengers are a much more traditional superhero team complete with costumes and codenames. Runaways always had more females than males, while the Young Avengers (being the more traditional team) always had more males than females, adhering to Two Girls to a Team. Runaways have a villainous lineage involving their parents and trying to atone for their sins. For comparison, the Young Avengers take on heroic legacies. Runaways were based in Los Angeles, Young Avengers were based in New York City.
This is highlighted in the Civil War event, where the two crossed over for the first time. While both were opposed to the Superhuman Registration Act, they entered and ended the war in different ways. The Young Avengers, based in New York, were in the epicenter of the conflict and were acutely aware of the act from the beginning, and in fact were captured by S.H.I.E.L.D. while fighting against it, but rescued by Captain America and recruited into the Secret Avengers. Whereas the Runaways, based in Los Angeles, had comparatively few superhumans and were far away from the resistance, unable to make their presence felt, and it was only when S.H.I.E.L.D. were deployed to LA to capture west coast superhumans did they take action. Upon meeting each other, it was a rocky start as the Young Avengers wanted to help and recruit the other to the Anti-Reg side, but the Runaways distrusted them, leading to a clash of egos (the Runaways weren't exactly fond of the Young Avengers beforehand, either). In the end, they were able to work together and parted on amicable terms. However, the Runaways decided they wanted no part in the conflict afterwards and became neutral, whereas the Young Avengers stayed as part of the war until the very end.
Kanan: Commander Grey and Captain Styles are both clone troopers under General Depa Billaba, and together make up half the survivors from her first Battalion. They are however very different from each other and Grey is affiable, kind and devoted to Billaba, while Styles is sarcastic and devoted to the Republic. Grey ends up being the only known clone to fight off Order 66 (though only after killing Billaba), but when he tries to point out just how messed up the order is to Styles the captain refuses to listen and continues trying to kill Caleb so Grey sacrifices himself to ensure their transport is destroyed, killing all the clones hunting the Jedi apprentice.
Knights of the Old Republic has its hero Zayne and villain Haazen. Both were incompetent Padawans, routinely humiliated, but best friends with the most outstanding member of their class. But while Zayne accepts that he's going to flunk, Haazen expected to skate by on his friend's coattails. Zayne didn't blame anyone for his expected failure; Haazen blamed everyone in the Galaxy except himself. While Zayne was ready to find a new path, Haazen trailed after his friend and grew so bitter that he betrayed him to his death. Then Haazen spent the next decades trying to rot the man's legacy, while Zayne is so true to Jedi principles he outdoes most of the actual Jedi in the story.
Elorin to Praxton in White Sand. While Praxton is a Fantasy-Forbidding Father who attempts to bend rules to force Kenton to resign from his aspirations and resorts to ad persona to humiliate him, Elorin is more worried about Kenton's safety, yet ultimately states that it's Kenton's decision and enforces the rules to let him participate in the exam.
DC Rebirth and it's stories have slowly built up a idealistic vs cynical conflict between two of DC's most iconic characters: Superman the alien with godlike powers who embraces humanity, and Doctor Manhattan, a human with godlike powers who has lost his humanity, the focus on this being the 2017 Doomsday Clock event.
K'Kruhk to Darth Krayt in Star Wars: Legacy. Both were Jedi who survived Order 66 by killing every clone trooper around them, and went on to lay low in the Dark Times that followed. Both became instrumental in rebuilding their respective orders, Krayt by rebuilding it from scratch on Korriban, and K'Kruhk by training Jedi in secret until Luke came along, and both eventually ascended to become rulers of the entire galaxy. Whereas K'Kruhk survived by hiding and finding those he could trust, Krayt survived by killing any witness, and whereas Krayt was an Evil Overlord who held absolute power, K'Kruhk is a Benevolent Mage Ruler who shares power with his fellow triumvirs.
On a faction-wide level, the Suppression Squad is this to the Freedom Fighters. The clue is in the name, suppression versus freedom. Otherwise, they are literally the same ensemble of characters. The SS come from a planet in an anti-verse of sorts called Moebius (the extra 'e' in the name no doubt referring to it being evil), while the FF live in Mobius. All of the evil equivalent characters (like Evil Sonic/later Scourge to regular Sonic, etc.) share many similar character traits with the originals, but are evil, cruel, selfish and suppressive.
Scourge and Sonic deserve special mention considering how many different ways they contrast each other. Both being speedsters who try to look cool, they otherwise couldn't be any more different. Scourge is a purely spiteful, egotistical Jerkass while Sonic is a Jerk with a Heart of Gold hero type. Scourge also succumbs to an inversion of Evil Feels Good with his super form. Despite its power, he feels horrible when he's in that state, as opposed to Sonic who feels great when in his super form. A back and fourth Not So Different speech between the two drives this home. What makes them different overall is how Scourge fell victim to a whole "One Bad Day" occurrence, while Sonic has a certain level of selflessness and decency that Scourge lacks. If not for those things, they would be pretty much the same.
Sally Acorn and Fiona Fox. One is a Freedom Fighter, the other an ex-Freedom Fighter. Sally is loyal and trustworthy while Fiona has a tendency to turn on people she's aligned with. Sally is a well respected leader amongst the heroes and often plays the role of Cool Big Sis to some of the younger male characters like Tails. Fiona exploits the feelings of male characters to her advantage, much to Sally's annoyance and disgust, as displayed when Sally gut punched her for toying with Tails. Sally is a Tomboy who subverts the role of Princess Classic by leading the Freedom Fighters as a competent battle strategist and tactician, with an androgynous appearance. Meanwhile, Fiona is a bit more of a GirlyGirl with a knack for using her feminine charms to manipulate male characters, with a relatively feminine appearance. Both are tough Badass Normal girls (in the context of the Sonic universe, anyway) who often find themselves as rivals whenever the Destructix or whatever group of villains Fiona has teamed up with crosses paths with Sally's Freedom Fighters.