I think my number one fear is having to endure excruciating pain.
There's the obvious fear of being alone. Or having anyone I love die.
Insane people also scare the breesus out of me. I can't count how many times I've had nightmares where my mum goes insane and tries to kill me.
Also (this is really conceited but whatever) any kind of deformity. In my anatomy class two years ago I seriously had to put my head on the desk when we got to the skin diseases and burns slideshow.
Pretty much any kind of insect or arachnid, aside from the obvious fly and mosquito. I've come across two house centipedes (do not google image house centipedes
you will cry) in the place where I live currently and as soon as I saw them I ran up (or down) the stairs. Also once there was one of those huge ass fuzzy bumblebees in my kitchen and my mum wasn't home to kill it, so I threw on my ski jacket and jeans and barely managed to kill it ;^;.
Lastly, clowns. Though this fear was more in my childhood. I still remember a dream I had when I couldn't have been older than 3 or 4 where I was walking down my hallway where I lived, and in that hallway there was a bar-ish area, anyway I could see my family watching TV (it was really like the ending thing for the Simpsons where the guy goes "sh" in the theater, that's what it looked like) and I passed the bar area and two clowns grabbed me and took me behind the bar and they were puppet clowns (if you've seen Poltergeist then you know what I'm talking about) and they just started choking me by extending their arms and stuff. And I tried to shout out to my family who had their backs to me, but they never heard me. I'm seriously amazed I still remember a dream I had when I was 3 or 4.