There are many, but favorites are:
Homecoming, Season 10, Episode 4.
Red, Season 2, Episode 4.
Accelerate, Season 2, Episode 21.
Instinct, Season 8, Episode 9.
The first season premiere of Season 10.
Salvation, Season 9, Episode 22 or 21. (Last episode when Clark is stabbed with the blue kryptonite dagger and kinda dies.)