Your mileage might vary, but I found "Dead Space" disturbing. It was hard for me to think quickly enough while being rushed by a half-dozen of those horrors.
Ah, I forgot Dead Space. Not particularly scary, but incredibly tense and atmospheric (Especially on the higher difficulties). Would definitely recommend to all fans of horror.
As for FEAR, I found the first game mind-numbingly tedious and repetitive. Ironically enough, the supposed "not scary at all" FEAR 2 managed to freak me out several times. I guess either FEAR's brand of horror gets better with its graphics or I'm just an odd case.