Mine are:
- Wrong Turn 1-3 (3 being my favorite.)
- Saw 1-3 (Though, 10 was fun.)
- Terrifier 1-3 (These are amazing.)
There are actually a bunch of movies in the "series". But I think only the first two have real continuity, but they all star the same two actresses.
Edit: Looked it up, and it's three movies. One is a prequel.
Never saw the third.