As of Generation 8, in (mostly) Pokedex order:
Regular evolutions
- Onix (Rock/Ground) into Steelix (Steel/Ground)
- Scyther (Bug/Flying) into Scizor (Bug/Steel)
- Scyther (Bug/Flying) into Kleavor (Bug/Rock)
- Pupitar (Rock/Ground) into Tyranitar (Rock/Dark)
- Kirlia (Psychic/Fairy)* into Gallade (Psychic/Fighting)
- Azurill (Normal/Fairy)* into Marill (Water/Fairy)
- Surskit (Bug/Water) into Masquerain (Bug/Flying)
- Nincada (Bug/Ground) into Ninjask (Bug/Flying)
- Nincada (Bug/Ground) into Shedinja (Bug/Ghost)**
- Swablu (Normal/Flying) into Altaria (Dragon/Flying)
- Skorupi (Bug/Poison) into Drapion (Poison/Dark)
- Fletchling (Normal/Flying) into Fletchinder (Fire/Flying)
- Skrelp (Water/Poison) into Dragalge (Poison/Dragon)
- Dartrix (Grass/Flying) into Decidueye (Grass/Ghost)
Regional forms
- Exeggcute (Grass/Psychic) into Alolan Exeggutor (Grass/Dragon)
- Mime Jr. (Psychic/Fairy) into Galarian Mr. Mime (Ice/Psychic)
- Rufflet (Normal/Flying) into Hisuian Braviary (Psychic/Flying)
- Dartrix (Grass/Flying) into Hisuian Decidueye (Grass/Fighting)
Mega Evolutions
- Charizard (Fire/Flying) into Mega Charizard X (Fire/Dragon)
- Gyarados (Water/Flying) into Mega Gyarados (Water/Dark)
- Altaria (Dragon/Flying) into Mega Altaria (Dragon/Fairy)
Different Forms***
- Plant Cloak Wormadam (Grass/Bug) / Sandy Cloak Wormadam (Ground/Bug) / Trash Cloak Wormadam (Steel/Bug)
- Rotom (Electric/Ghost) into Rotom Heat / Frost / Wash / Mow / Fan (Electric / Fire / Ice / Water /Grass / Flying/Ghost)
- Meloetta (Normal/Psychic) into Meloetta-Piroutte (Normal/Fighting)
- Hoopa-Confined (Psychic/Ghost) into Hoopa-Unbound (Psychic/Dark)
- Pom-Pom Oricorio (Electric/Flying) / Pa'u Oricorio (Psychic/Flying) / Baile Oricorio (Fire/Flying) / Sensu Oricorio (Ghost/Flying)
- Single Strike Urshifu (Fighting/Dark) / Rapid Strike Urshifu (Fighting/Water)
- Calyrex (Psychic/Grass) / Ice Rider Calyrex (Psychic/Ice) / Shadow Rider Calyrex (Psychic/Ghost)
*Before Generation VI, the Fairy type didn't exist, meaning this entry is not true prior to Generation VI.
**Nincada does not technically evolve into Shedinja, but it's close enough that I decided to include it.
***While form changes aren't evolutions, I'm including them, as it's still helpful to have. Necrozma is originally a single type, so its forms aren't on here, even though they're dual types.
A bit of random trivia: Swablu --> Altaria --> Mega Altaria is the only dual typed Pokemon line to change types three times upon each evolution.