Tempest and Blackwing from the New Warriors. After going out to fight crime together, they come home to take care of their kids. New Warriors also had Nova and Namorita, Firestar and Justice, and Night Thrasher and Silhouette.
Thor and Sif, both Norse warrior gods. This comes in handy when Thor is time-sharing Don Blake's body, and is not up to fighting giant robots because he's busy trying to fish Mjolnir-in-stick-form out of the gutter where he accidentally dropped it.
Spider-Man and Mary Jane Watson in Spider-Island where MJ gets his powers and isnt turned into a spider-humanoid. This was due to MJ building up an immunity to Peters DNA thanks to the all times they... shared a toothbrush.
Cyclops and Phoenix, combining his optic blasts with her potent psychic abilities. Many stories featured them charging into battle together, hand-in-hand, and blasting their way through opponents.
Cyclops and Emma Frost became this, after the death of Phoenix. They tend to lead from the front line together, though not nearly as effective a team as the above couple were.
Rogue and Gambit have had a long, rocky history of on-again-off-again dating. They're both powerful fighters in their own right, and work well together in battle. During one storyline Rogue and Gambit have their powers switched in the middle of a battle and since they know each other so well no effectiveness is lost. When Happily Married, both Gambit and Rogue take an entire army of the Shi'ar empire together in their solo series.
Shadowcat and Colossus have gone through multiple breakups and reunions, and have unique teamwork taking advantage of their powers. On occasion, he's been known to throw her at opponents to great effect. The Age of Apocalypse AU took this up a notch, making them a married couple that terrified quite a few people with their ruthlessness in battle.
Rictor and Shatterstar went from being long-time ambiguous friends, to an official couple when reunited. One has earthquake powers, while the other is a genetically engineered Super Soldier.
Havok and Polaris are another classic of the series, and are both powerhouses in their own right. They've led multiple teams together, and gone through many rough periods in their rocky relationship.
On the villains side Titania and Absorbing Man were this for a while. They got married. The Hood and Madame Masque were another example. The Infinity event introduced yet another married villain couple - Corvus Glaive and Proxima Midnight, notable in that they manage to defeat the Hulk when fighting in tandem, as well as held their own against Captain America, Hyperion, and Captain Marvel.
The Authority Apollo and Midnighter, a rare male/male example. That they're unstoppable warriors somehow makes it all the more adorable when they drop the badassery for a cuddle. Also, should you mess with one, expect the last thing you ever see to be the other one dismembering you.
Although DC prefers non-costumed spouses/significant others, there are a few qualifiers:
The original incarnations of Hawkman and Hawkgirl.
Villain example: Cannon and Sabre were assassins working for opposing gangs who decided to kill each other's bosses and merge the two organisations into one with themselves on top. When that panned out, they bought a beach house together and went freelance.
Nightwing and Oracle are a Mission Control style pair because Oracle isn't usually in the field but still fights her battles behind-the scenes. There was also that tension between him as Robin and her as Batgirl...
Cosmic Boy and Night Girl are superheroes on the same team who fight beside one another.
Lightning Lad and Saturn Girl are another couple on the same team that battles together. They eventually went on to get married and have children.
New Teen Titans: Adeline and Slade (Deathstroke) Wilson, till his double life got their son kidnapped and rendered mute, then she shot out his eye (she was trying to kill him, but enhanced reflexes saved his life, if not his eye).
Zatanna and John Constantine. Though both are worlds (or versions) apart, both make up for a Badass Magical Couple. Then John Constantine is put back into the DC Universe and the two get back on their relationship.
Knuckles the Echidna and Julie-Su. Knuckles has Super Strength, while Julie-Su's an expert with firearms (and also not too shabby herself at hand-to-hand combat).
Sonic and Sally; the cartoon adaption's opening theme shows them blowing up a Robotknik base together. She's in his arms by the end of it.
Bunnie and Antoine are a husband and wife team; one is a badass cyborg and the other a master swordsman.
At the end of Watchmen Silk Spectre II and Nite Owl II have married, and from their conversation it's clear they plan to work together as illegal masked vigilantes.
Invincible aka Mark and Eve work well together, even before they get married have a daughter together. Best showcased one time when Mark and Eve massacred a bunch of killer aliens on a family picnic together with Terra.
Ball and Chain features Edgar and Mallory Bulson, alias Thunderball and Chain Lightning. Their powers are dependent upon their physical contact and proximity, which is inconvenient since their relationship was over when they got them. Still, they get it together in the end - because they'll always be there for each other.
"She's my valkyrie. My warrior woman. The fire. It'll burn us both."
Scott Pilgrim and Ramona Flowers; their relationship is the basis of the all the fights with the evil ex boyfriends.
ROM Spaceknight: ROM and Starshine inspired a crowd into resistance fighting together as seen here◊
Dungeon: The Early Years: Hyacinthe and Alexandra, although Alexandra is his mistress, became this when Hyacinthe lost his innocent vigilantism persona and became the head of the city's underground with Alexandra as her best assassin. Hyacinthe's first kill was a target Alexandra was struggling with.