The user can animate corpses and dead beings, making them able to move and react. They are usually under the user's control, but because the corpses are likely mindless, they have to be carefully monitored. However, some users may be able to create sentient or semi-sentient undead.
Benny Weir (My Babysitter's a Vampire); using a reanimation potion
Marie Laveau (American Horror Story: Coven)
Pylich (TF2 Freak)
Matoro (Bionicle); via his Kanohi Tryna
Morgana (The Sorcerer's Apprentice)
Hendrickson (Nanatsu no Taizai)
Melascula (Nanatsu no Taizai)
An Shigeng (The Four)
Riza Brenner/Momiji Tenma (Dies Irae/Kajiri Kamui Kagura)
Siren (Bioshock Infinite)
Herbert West (Herbert West the Re-Animator)
Majorita (Disgaea 5)
Hoodoo Mama (Wild Cards)
Charmcaster (Ben 10); limited to small animals
Elise (Azure Striker: Gunvolt)
Imhotep (The Mummy)
Christopher Muse/Triage (Marvel)
Steven/Rose Quartz (Steven Universe)
Jesus (Madness Combat)
Demongo (Samurai Jack)
Yatsufusa (Akame Ga Kill!)
Orb of Rafuk (The Life and Times of Juniper Lee)
Ovu Mobani (Buffy the Vampire Slayer)
Idol of Granath (Angel)
Resurrection Stone (Harry Potter)
T-Virus (Resident Evil Series)
Blacklight Virus (Prototype)
Reanimation Potion (Sankarea)
Kanohi Tryna (BIONICLE)
Element 115/Divinium (Call of Duty: Black Ops series)
Green Dip (Catscratch)
Yamamoto (Bleach) reanimating ten trillion skeletons of victims he killed.
Kagura (InuYasha) using her wind to utilize her Corpse Dance, controlling corpses as puppets.
Sō'unga (InuYasha) can reanimate entire army of corpses to serve as its minions and summon the souls of the dead...
including Setsuna Takemaru who So'unga chose as its host.
Orochimaru (Naruto) uses Summoning: Impure World Reincarnation to resurrects Hashirama Senju, the First Hokage, and Tobirama Senju, the Second Hokage.
Kabuto (Naruto) demonstrating the reanimating ritual.
Sohaku Kago (Tenjho Tenge) turned Fu Chi'en's corpse into a zombie, having him fight with his abilities intact.
Ovu Mobani (Buffy the Vampire Slayer) reanimates a nearby corpse.
Rea (Sankarea) holding a glass of the Reanimation Potion.
Stevie (Smosh) has the power to reanimate the dead with the power of love.
Jesus' (Madness Combat) most infamous power in the series is the ability to resurrect the dead. Up until Madness Depredation, he would often resurrect Hank's victims into zombies, in order to fight Hank. Although they do not possess better fighting skills, they are much more resistant to attacks than they are normally.
Element 115/Divinium (Call of Duty: Black Ops series) was the key material used by Group 935 to create several weapon programs, one of which was the undead army super soldier program for the Third Reich.