Mine are a little different. I don't watch a lot of horror as I just don't like the gross-out and jump-scare stuff that's so prevalent these days.
Luckily, I can see most jump-scares coming so I'm largely unaffected and just have to prepare for my wife to shriek and possibly lacerate my arm =0), but...
The Forgotten. When Julianne Moore and the guy are driving and talking and everything is quiet and calm, then WHAMO they get t-boned by a truck, coming toward the camera. That made me jump nearly backward over the couch! My heart was beating so hard it felt like I'd just sprinted a mile. Hooboy.
The other one is more the deep, core fear type: The nuke/playground scene in T2.