Atrax and Myrmeleo, members of the Traptrix archetype, both resemble their pets/host bodies. Atora's braids can be seen as the limbs of a spider and her decorations resembles a spider's fangs. Myrmeleo could be seen as an ant lion because her hair decorations resemble an antlion's jaws.
Rinyan is Lumina's pet cat, as Rinyan is wearing Lumina's headdress, necklace, and one armband on her tail,
The Beano, the comic Dennis appears in, loves this trope. There's Rasher, a pig covered in spiky bristles; Pup Parade, featuring the pets of the Bash Street Kids; Roger the Dodger used to have a pet called Joe Crow with the same tuft of hair/feathers; and, in the silliest example, Cuthbert Cringeworthy, the Bash Street school swot, looks like Teacher. Because he's the teacher's pet.
Desperate Dan, the cover character in sister-comic The Dandy has a dog which shared his prominent chin.
Dilbert and his dog Dogbert both wear the exact same set of glasses and have the same mouthless faces.
There was a comic strip where Jon and Garfield commented on this trope, with increasingly bizarre lookalikes. This culminated with some guy who looked like a bird in a suit and his pet canary.
Another one had Garfield deliberately doing this himself to people walking in the park by following them around and mimicking their mannerisms. This went sour when one fat guy caught him in the act, though:
Garfield: I thought fat people were jolly...
In Dennis the Menace (US version), the fur on the top of Ruff's head resembles Dennis' hair.
This was most noticeable in Footrot Flats when The Dog went to a dog show and saw heaps of dogs who resembled their owners. Although The Dog doesn't resemble Wal at all, there is a degree of resemblance between Wal and Major the pig dog (possibly coincidental) and also between the 3 Murphys and their dogs Tiger, Wolf and Cream Puff.
In Beetle BaileySgt Snorkel and his dog Otto look markedly similar, down to Otto wearing a uniform and walking on his hind legs.
In one Mafalda strip, three persons who looked a lot like their dogs are laughing at Mafalda because she has her pet turtle Burocracia on a leash like a dog. She angrily yells at them for being "racist".
Scruffy has a scene displaying this. At the end, a number of dogs are adopted by people who resemble them.
In Mulan, Shan Yu looks very much like his pet falcon - right down to hawk-like eyes (while the bird has eyes with little irises just like a human).
Hiccup and Toothless in How to Train Your Dragon and How to Train Your Dragon 2. Both are crippled with a limb which is fixed on a prosthetic. Both are smaller than their compatriots, fitting Weak, but Skilled and even share similar fun-loving, snarky personalities. By the end of the second film, the scrawny Hiccup inherited the title Chieftain of Berk from his massive father to become the leader of his people while the lithe Toothless challenged Drago's colossal Bewilderbeast and succeeded, becoming the Alpha and leader of his people.
Films — Live Action
The new version of The Shaggy Dog showed comparisons of the cast with animals that resembled them.
There's a children's picture book called It's Easy to See Why in which a girl enters her dog into a dog show and is the only owner there who doesn't bear a striking resemblance to her pet. Her dog wins, though... because he looks just like the judge.
The Lord of the Rings: Treebeard says something similar to this in The Two Towers about Ents and trees becoming more like each other.
Grace Lockwood from the A-to-Z Mysteries book The Falcon's Feathers looks very much like a falcon when she reads an issue of Falconry Today in a picture at the end of Chapter 5.
Jane Eyre: Mr Rochester snarks that his dog Pilot looks more like him than his ward Adele Varens. Adele's biological mother claimed he was her father, but Celine Varens was cheating on him and Adele looks nothing like Mr Rochester.
In a variant, a murder victim on Bones who'd owned a chicken-processing plant somewhat resembled the chickens he worked with, due to a poultry-borne fungal infection which deformed his sinuses.
In an especially bizarre example, on 3rd Rock from the Sun, Wacky Guy Harry's pet from the home planet, "Pickles", shows up unexpectedly on Earth, and also took the form of a rubber-faced manic human in ugly sweaters.
In Jake and the Fatman, the aforementioned "Fatman" (a no-nosense and very large prosecutor) has a pet bulldog named Max who looks quite a bit like him.
Barbie sets that give the dolls pets have a tendency to match fur and hair color — Barbie with a blond-furred dog, Teresa with a brown-furred dog, etc.
Not exactly a pet, but close enough. In the Sci-Fi chapter of Live A Live, the main character, a robot named Cube, is always wearing a baseball cap and glasses, that its owner also wears, this has the side effect of making it very cute (although this chapter is so unrelentingly bleak and moody that Cube's appearance actually provides some small relief).
The Medic and his doves (especially Archimedes) in Team Fortress 2. They were both stuck in lucrative but ultimately unsatisfying careers (wedding dovery and medicine, respectively), but met when Medic hijacked a catering van at the Prime Minister's wedding. His doves share his enthusiasm for blood, and when perched on his shoulder as an in-game item, Archimedes blinks and opens his mouth whenever Medic speaks (due to the item being tied to Medic's facial flexes).
Warlords in Pokémon Conquest, when transformed, have armour that deliberately invokes their perfect partner's appearance. With humanoid Pokémon, you usually end up with a cosplayer's dream costume (Fūma Kotarō almost exactly resembles his Zoroark). More... articulate Pokémon have simple accessory references (Kanbei gets something straight off of the Light Emperor to resemble his Chandelure)
The short film Pig Me revolves around this trope.
Many of the lusus in Homestuck resemble the trolls they're the guardians of, especially in horn shape. This is most obvious with Tinkerbull, Tavros' guardian who shares his horns, and the Virgin Mother Grub has Kanaya's horns and lips.
In Charlie Dog's debut cartoon Little Orphan Airedale, he plays with this trope by mimicking the faces of people passing by until he sees Porky Pig, showing that both of them have similar faces.
In Rugrats, Angelica's pet cat Fluffy is designed to look like her. One Nickelodeon UK advert narrated from Spike the dog's perspective lampshaded it.
In the episode of Doug where everyone goes to the dude ranch, the horses assigned to each character have an unnerving habit of resembling them. Of particular note are Romulus and Remus, a pair of purple, bespectacled horses for the purple, bespectacled pair of Al and Moo Sleech.
In Handy Manny, Mr Lopart's cat, Fluffy, has brow-whiskers stretching across her forehead in the same manner as his combover.
In the Dexter's Laboratory episode "Dexter's Lab: A Story", Dexter finds a stray Laborador retriever. At the end the dog is reunited with its actual owner, a manic surfer dude who looks (and acts) very similar to him.
In the episode "McLeish Unleashed" of Pound Puppies (2010), Milton Feltwaddle (who took over when McLeish was promoted) instituted a system where dogs and humans were matched up by how similar they looked to each other. This didn't work out so well, however.
Zigzagged with Applejack and Winona (a collie who's as athletic as her owner but much more happy-go-lucky and silly) and Rarity and Opalescence (a white Persian who likes quality fashion and treatment as much as her owner but is a lot less sweet-natured) and played straight with Twilight and Owlowiscious (an owl).
Dozer the bulldog from Mister T has the same mohawk as Mr T.
Rhea, the second-largest moon of Saturn, is the only moon in the Solar System to actually have rings around it.
Similarly, Ganymede, the largest moon in the Solar System, is also the largest moon of Jupiter, the Solar System's largest planet.
The moon Triton is blue like its parent planet, Neptune.
Inverted by our very own Moon, usually defined as a gas giant's moon in a small rocky planet's orbit.
According to this website, there's a strong correlation in the British Isles between the prevalence in an area of ginger cats and the proportion of that area's population who have ginger hair.
A sort-of-informative show in Germany tried to prove this by showing pictures of dogs, then of owners to random passengers, asking them to arrange the pictures. Most of them were right. However, this show is notorious for only showing the results they found interesting, so who knows.
A semifamous meme in which photos or screencaps of Benedict Cumberbatch are compared to photos of otters bearing the same pose and/or expression. A similar phenomenon has sprung up around his fellow actor Martin Freeman, comparing him to hedgehogs instead.
The first American cat breeder to raise the Khao Manee, a white breed of cat from Thailand that's prone to heterochromic eye color and deafness, has one blue and one brown eye. Her husband and daughter are also deaf.