Yeah, put me down for John Carpenter's The Thing* as well.
Others I enjoy:
Romero's Night of the Living Dead / Dawn of the Dead / Day of the Dead
Pontypool (zombie-type, "Shut Up or Die")
The Return of the Living Dead (1985)
Shaun of the Dead
Invasion of the Body Snatchers (197
Alien / Aliens
Jaws
The Descent
The Mist
The Ruins
Otis (dark humor)
30 Days of Night (very Thing-formula, but brutal)
* I'm less on board for the Thing prequel that's being made that apparently shows what happened at the Norweigian research site-- only requires a hint of imagination to piece that together while watching the original.