Commander Vora and her husband General Lagan from Art Of Domination had been married for 20 years at the start of the story, and are very much in love.
The Bird Feeder has Darryl and Edna, two cardinals, because cardinals (supposedly) mate for life.
Erika and Matt of DAR!: A Super Girly Top Secret Comic Diary, both in the webcomic and in real life. Erika herself says that her years with Matt have been the happiest time of her life. Made even more noteworthy by her originally being a 100% lesbian with a very dim opinion of "hetero-normativity" until she met Matt.
Donovan and Miranda Deegan in Dominic Deegan who still get busy every once in a while.
In Fans!, Rikk's parents are happily married. Later Rikk's marriage to Alysin proved to be rather tumultuous (Aly's tendency toward self-loathing led to her wanting to break it off with Rikk at one point). Rikk and Aly (and Rumy) are a happily married couple triple.
Fox and Collin of Friendly Hostility. Fox's parents (and Rafi) have been happy together for decades.
Master Payne and the countess may have the occasional argument, as can be expected of a couple trying to keep themselves and their circus troop alive in the dangerous wastelands, but even their arguments generally devolve into flirting and they do whatever they can to keep each other happy and relatively safe.
Old Man Death and the wild princess both stepped away from their former wild lives in order to spend the rest of them together in their youth and are still deeply enamored and happy with each other in their old age, though she never did like his ubiquitous hat so she'll be pleased Maxim tricked him out of it.
The Dunkels from El Goonish Shive have a peaceful, happy home life. It's made sweeter by a small panel's implication that Elliot was a mistake that happened too early, but they soldiered on through the hardships.
Mr. and Mrs. Cake from Slice of Life, just like their cartoon counterparts. They shamelessly refer to each other with cutesy nicknames in public, and never get angry or frustrated with each other, even when dealing with their more troublesome customers or suppliers.
Mrs. Cake: "Well, let's get this over with, ginger-beer." Mr. Cake: "We should probably knock, sugarpie." Mrs. Cake: "Oh, one of us should, toffeebean." Mr. Cake: "Sometime soon, fizzypop."
Fred and Faye MacIntire, Davan's parents from Something*Positive. Faye dies peacefully of old age, and since most characters are based on the cartoonist's life, his mom started looking at him funny. The strip after this had the tagline at the bottom: "I got a very annoyed voicemail from my mother today. I wonder why?"
Also Aubrey and Jason; they are also based on real people, though those people are not a couple in real life.
Stand Still, Stay Silent: In the Finland segment of the prologue, the two married couples shown seem to be going along quite well. Tuuli and Eino are shown to be on the same Crazy Survivalist wavelength, while "usually 'dying' from something" Saku responds to his wife coming to comfort him during a bout of seasickness by telling her he's always loved her.