Well, in the past i've been very scared of riding new coasters IE Nemesis and Rita however, I don't ever get scared of riding new rides now, have overcome that fear.
One coaster I reckon I would crap myself on would be X, does look fairly scary. Going down those drops at weird angles and all that. Also, any HUGE drop towers would scare me. Done ToT Florida and Detonator at Thorpe which I both love (ToT one of my top rated) but say the one at Port Aventura or Apocalypse, they look MASSIVE and I would probably get soooo scared, but would still go on them.
Also, I do still get scared on Oblivion which is why it remains my no 2 coaster. The way it intimidates you and looking down that drop for 3 seconds is horrific. Found the best way to ride it a couple of months ago, hands behind ya back on the drop, fly out of your seat, major airtime
Dan