Two things are noteworthy for me.
First time I played Bioshock was in the wee hours of the morning. I forget which area of Medical I was in, but there's a splicer who jumps out of a cupboard next to some stairs and pooled water. Anyways, in my sleep deprived state I was incredibly jittery, and freaked out on this splicer when I rounded the corner. I ignited him on accident, and he promptly ran screaming across the room, jumped down the short stairwell, and belly-flopped into the pool of water to extinguish himself. I was so freaked that I ran over and took my wrench to him numerous times before calming down and leaving.
Also, this scene from the Force Unleashed II [http://www.youtube.com/watch?v=furd6yGdNQo] startled me quite a bit. My reaction was essentially as follows: "What the crap is this? Did they say goron or whatever and send out a fucking raincOH MY GOD WHAT IS THAT!?"