Heights get me everytime, especially when the fall is a likely occurrence (ie. shingling a high pitch roof, looking over the edge of a tall building roof, being at the top of a 50 foot aluminum ladder with no one at the bottom and a with a huge bend from the weight). I will literally seize up, close my eyes and not move. If I am up high I have to have the utmost confidence in what I am standing on or I will lock up.
Spiders used to freak me out, but that subsided over time.
Sometimes you gotta chill and eat a [link=http://www.youtube.com/watch?v=HSCotdOh5WY]pickle[/link]