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)
Batman and The Joker. The Joker is possibly the only villain who Batman cannot defeat through his M.O.s of reasoned deduction and intimidation. The two are also philosophical foils in The Killing Joke. The Joker is a Nietzsche Wannabe who believes life is one big joke and the only way to deal with that is by giving in to madness. Batman is an Anti Nihilist who also believes life is meaningless but decided to create his own purpose.
Batman and Deadshot is another example. Both come from affluent backgrounds, but while the former had to deal with the loss of their parents, the latter had to deal with the loss of his brother over the abuse of said parents. While Batman is an Anti-Hero who fights crime for the sake of justice, Deadshot is an Anti-Villain who often kills those worse than him for the sake of money. It's also exemplified by their fighting styles — Batman is a gadget/martial arts master who Doesn't Like Guns, while Deadshot is a Gunslinger with Improbable Aiming Skills.
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.
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 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.
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.
Dick Grayson shows us how Bruce might have turned out if he'd been adopted by a loving family after his parents' murder instead of growing up in Wayne Manor with only his butler for company. Where Bruce is moody, brooding, suspisicous of others, somewhat emotionally stunted, and a bit of a loner, Dick is cheerful, upbeat, optimistic, a born showman, and one of the most trusted and well-liked men in the superhero community. And where Bruce is still continually haunted by his parents' murder, Dick has largely come to terms with his parents' death and learned to move forward. As the superhero Nightwing, he also wears a simple jumpsuit with an eye-catching bright blue motif, in contrast to Bruce's somber black cape and cowl. Among the Robins, he's known as "The Charming One".
Jason Todd shows us how Bruce might have turned out if he'd been born into poverty instead of the wealthiest family in Gotham. Where Bruce had the advantage of growing up in a safe home environment after his parents' death, Jason was forced to live on the streets, where theft and violence were a way of life. Even after Bruce takes him under his wing, he never quite lets go of the inherent anger of feeling forgotten by society, and grows into an impulsive young man with a noticeable propensity for violence. As the vigilante Red Hood, he outright rejects Bruce's refusal to kill criminals, choosing to deal out justice with a gun. Among the Robins, he's known as "The Brutal One".
Tim Drake shows us how Bruce might have turned out if he'd had a more stable childhood, and had gotten a chance to choose crime-fighting instead of being pushed into it by tragedy. Unlike Bruce and the previous Robins, he starts out as a generally normal middle-class kid with no special training or experience in combat, but he voluntarily offers himself up as Bruce's sidekick after using his natural detective skills to deduce his true identity. As the superhero Red Robin, he even becomes the only person besides Bruce to earn the moniker "Detective" from Ra's al-Ghul. Among the Robins, he's known as "The Clever One".
Damien Wayne shows us how Bruce might have turned out if he'd never gotten a chance to have a carefree childhood or loving parents before devoting himself to becoming the perfect warrior, and had simply been molded into a killing machine when he was still a child. As a Child Soldier born into the League of Assassins, he shows us Bruce's Training from Hell taken to its disturbing logical conclusion. Where Bruce at least had the luxury of choosing to put himself through years of physical and mental training when he decided to become a crime-fighter, Damien was pushed into it by the adults in his life, and essentially became a Living Weapon used in other people's conflicts. Where the other Robins learned to become better crime-fighters under Bruce's tutelage, Damien just had to learn how to have normal human relationships, and how to discern between crime-fighting and simple murder. Among the Robins, he's known as "The Deadly One".
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.