i have a lot! lol
-when my cell phone vibrates in my pocket

-when glass breaks
-when a balloon pops
-when someone pokes me when im reading
-when our school bell rings...
-in the middle of class, if someone drops a book really loudly and breaks the silence (i got in trouble for screaming. hehe.)
-when i don't know someone is next to me, and then they say something in my ear
-if someone jumps out at me while im coming out of the bathroom...

-when my siblings pull pranks on me
-when i get an IM, it makes this popping noise
-when the house telephone rings and im standing right next to it XD
-when my dog barks reeeeeeeeeeeallyl loud while im holding him
-if im in the pantry and i get a bag of chips out, and then i drop it, i scream

-if someone pokes/taps/touches me when i dont expect it
-when an air horn blows
-if those annoying talking smileys scream at you!!!
i think that's pretty much it.... but i think there is more.
(if you haven't noticed i get scared easily

)