Unless the user can affect matter while intangible or uses an object, materializing inside someone is a quick way to lose a limb.
Ghostfreak (Ben 10 Series)
Zs'Skayr (Ben 10 Series)
Bigchill (Ben 10 Series)
Ghost Soldier (DC Comics)
Martian Manhunter (DC Comics)
Miss Martian (DC Comics)
Speedsters (DC Comics/The Flash)
Pathfinder (DC Comics)
D.L. Hawkins (Heroes)
Shadowcat (Marvel Comics)
Vision (Marvel Comics)
Mirio Togata (My Hero Academia)
Obito Uchiha (Naruto)
Akua Shuzen (Rosario + Vampire)
Whisper Men (Doctor Who)
Edith Brennan/Mama (Mama)
Vision (Marvel Cinematic Universe) using his intangibility to attack an Ultron Sentry.
Using the Jigen-Tou, Akua Shuzen (Rosario + Vampire) turns intangible to slice through an opponent.
The Vision (Marvel Comics) demonstrates two forms of intangibility during combat.
Obito (Naruto) incorporates his intangibility into his fighting style to trick enemies into attacking him, before striking at the right moment.
Mirio Togata (My Hero Academia) has a Quirk, Permeation, that allows him to become intangible and travel through matter. He utilizies this in combat by phasing into walls/floors and popping out at random locations to surprise the enemy.