It´s only the colour or appearance but here´s a list!
Venusaur -Female's flower has a seed in it
Butterfree -Female has purple (black in Generation IV) spots on her bottom wings
Rattata -Female has smaller whiskers
Raticate - -:-
Pikachu -Female has a cut in her tail; in Black and White only, male has slightly less black on the front of his ears
Raichu -Female's tail lacks a point
Nidoran (F and M) -Female is bluish and male is pinkish
Zubat -Female has smaller fangs
Golbat - -:-
Gloom -Female has single spot on each bud
Vileplime -Female has larger and fewer spots on her potals
Kadabra -Female has smaler whiskers
Alakazam - -:-
Doduo -Male has black necks and female has beige necks
Dodrio - -:-
Hypno -Female has larger fur collar around neck
Rhyhorn -Female has larger fur collar around neck
Goldeen -Male has a larger horn
Seaking - -:-
Scyther -Female has a larger abdomen
Magikarp -Male has beige whiskers and female has white whiskers; in Platinum only, the female has a smaller white band across its head
Gyarados -Male has blue whiskers and female has white whiskers
Meganium -Male has larger antennae
Ledyba -Female has smaller antennae
Ledian - -:-
Xatu -Female has fewer body stripes
Sudowoddo -Female has a smaller head "branch"
Politoed -Female has smaller cheeks
Aipom -Female has longer hair on her head
Wooper -Female has one antennae branch and male has two
Quagsire -Female has smaller back fins
Murkrow -Female has smaller "hat"; in Generation V, the female's right foot is a darker shade of yellow than the male's
Wobbufett -Female's mouth has lipstick
Girafarig -Female has larger yellow area
Gligar -Female has smaller stinger
Steelix -Female lacks an outer tooth on each side
Scizor -Female has larger abdomen
Heracross -Female has heart-shaped horn
Sneasel -Female has a shorter feather
Ursaring -Female has longer shoulder hair
Piloswine -Female has shorter tusks
Octillery -Female has smaller suction cups
Houndoom -Female has shorter horns
Donphan -Female has shorter tusks
Torchic -Male has a black speck on his rear
Combusken -Female has smaller feathers on her head
Blaziken -Female has smaller head feathers
Beatufly -Female has smaller red spots on her wings
Dustox -Female has smaller antennae
Ludicobro -Female has thinner stripes
Nuzleaf -Female has smaller head leaf
Shiftry -Female has smaller hand leaves
Meditite -Male's ears are higher than the female's
Medichan -Male has larger bulb on his head
Roselia -Female has longer body leaf
Gulpin -Female has shorter feather on her head
Swalot -Female has shorter whiskers
Numel -Female has larger hump
Camerupt - -:- s
Cacturnee -Female has a large diamond marking which occupies the space of two small diamond markings on the male
Milotic -Male has shorter hair-like fins
Relicanth -Female has smaller jaw guard
Starly line -Female has smaller spot on her forehead
Bidoof (our god) -Male has more tail curls
Bibarel -Male has bigger "mask"
Kricketot -Female has larger collar
Kricketune -Female has smaller moustache
Shinx -Female has blue hind feet and shorter mane
Luxio -Female has exposed ankle and shorter mane
Luxray -Female has shorter mane
Roserade -Female has longer cape
Combee -Male lacks a red dot on the lower face (because it can´t evolve I think)
Pachirisu -Female has shorter stripe on her head
Buizel -Male has two white spots on his back while female has one
Floatzel - -:-
Ambipom -Male has shorter hair on his head
Gible line -Male has grooved fin
Hippopotas -Male and female have inverted body colors from one another
Hippowdon -Male's body is brown while female's is dark gray
Croagunk -Female has higher "bandages"
Toxicroak -Female has a smaller throat sack
Finneon -Male has shorter tail fins
Lumineon -Female has larger fins
Snover -Female has more white on her midsection
Abomasnow -Female has longer chest fur
Weavile -Female has shorter ear "feathers"
Rhyperior -Female has smaller upper horn
Tangrowth -Magenta-colored part of the female's hands are longer
Mamoswine -Female has smaller tusks
Male has a pink mask on his head while female has a curved feather on the back of her head. Male has a green underside and female has a brown underside.
Male is blue and female is pink. Females have an eyelash on the bottom while males have one on the top. Males have lips that look like they are frowning while females have lips that look like they are smiling. Females have curved fringe. Females have more points on their crowns.
Male is blue and female is pink. Males have a facial covering resembling a moustache, while females have one resembling a fluffy collar. Males have diamonds on their inner tentacles and females have frills. Males' mouths are hidden inside the "moustache", while females have a visible one shaped like a heart. Females have two eyelashes and larger eyes while males have small eyes and one small upper eyelash. Males have more frills on their outer tentacles. Females have a larger crown-like projection on the top of their heads than males.
Male has a large mane with the kanji character, 大 (meaning "big" or "great"), visible on it with an overall stockier body with half-beige front legs. Female has no mane, but has long, flowing hair similar to a ponytail.
Male is mostly blue in color, with white highlights and green eyes. Female is mostly white in color, with blue highlights and yellow and red eyes.
Unlike most Pokémon, the moves Meowstic can learn vary by gender, with the male tending more towards support moves, and the female more towards attack moves.
Males have lowered eyes, a triangular mouth pointing upwards like a frown, and more black on its torso, made to resemble a suit. Females have wider eyes, a triangular mouth pointing downwards like a smile, and more white on its torso, made to resemble an apron.
Male Indeedee have higher Attack, Special Attack, and Speed, while female Indeedee have higher Defense, Special Defense, and HP. The two genders also have different moves.
Garchomp is the only pseudo-legendary Pokémon to have gender differences.
Fairy is the only type that lacks a Pokémon with gender differences.
Generation IV introduced the most Pokémon with gender differences, with a total of 31.
Generation VI introduced the fewest Pokémon with gender differences, with two.
Source and Time
Edit by KyogrePulse: Just adding Gen 8/Indeedee to keep this updated