I always hold my breath while driving by a graveyard. If for some reason I do breathe while going by, I have to cough to get the ghosts out of my lungs.
I only really have one and it’s strange. No opening of umbrellas indoors. I don’t know what’s supposed to happen if I do, but I don’t do it. Ever. I don’t even like it when others do it around me.
StG
I knock on “wood” using my male cat’s head. It started off as a joke, but now it’s a habit. Poor kitty.
[sub]And no, I don’t “knock” hard and he gets lots of love afterwards. 
[/sub]
I will not listen to “The Sweetest Thing” by U2. Since its release as a single, my hearing it in its entirety has led to a breakup every single time. In fact, I once thought that, after the song had been out four years and I’d been dating the girl for two years, it’d be safe to leave the song on the radio because everything else was commercials. Yah, she dropped me. That was about fifteen months ago, and I sprint to change the station should I hear those damn piano keys.
I won my first national title in a certain pair of socks. Those pretty babies have never been cleaned any way but dry since then. And they have responded to the pampering by delivering three more. They now rest in a plastic bag in a palce of honor in my sock drawer. When I am no linger fit for international competition, you can bet your sweet ass that they will be bronzed and sit on an oak pedestal on my nightstand.
Won’t walk under ladders nor step on graves. Wiccans also freak me out. I was cursed by one a while ago and ended up crashing my 84 fiero into a building the very next day.
Hmm I used to have a similar, but not as bad, thing about the song “Get Off” by Dandy Warhols. Hearing and enjoying it the first time seemed to be the starting point of a run of bad fortune. Fortunately it’s not a track you hear if you don’t want to much nowadays.
Volvos… can’t stand the bloody things, and won’t ride in one if I can avoid it.
I never liked the way they looked, and when I was in my early 20’s an idiotic friend of mine had one… I blew a number of my nine lives in that damn vehicle, most specifically the time we completely lost the brakes at the top of a very steep hill (at the bottom of which was a very busy intersection). I swore off of them after that.
Recently, knowing I was carless, a friend of mine offered me a free Volvo… I turned her down. When I had to explain the reason for this to my wife, well, let’s just say that now she thinks I’m retarded.
I really don’t have any superstitions but I love to violate the ones I know about whenever my parents are around; spilling salt, opening umbrellas indoors, shoes on the table (although that has good sanitary reasons not to do), walking under a ladder and so forth. Why? …it brings me good luck.
Personally I really don’t believe in superstitions but try letting go of a habit from many years ago. 
When I was a kid I heard on TV that it’s bad luck to say this one particular word (starts with P and lives in Antarctica) I forget if it’s in months with the letter R or in months without the letter R. So to be safe I never ever say that darn word. :o
Of course I always happen to glance at the clock at 11:11 or when the numbers have some specific relevance.
Oh and I think 13 is not unlucky but 27 is to be avoided. Apparently somebody noticed that it occurs frequently and devoted an entire site to it.
Well it can cause the wishstone to stop glowing, which is bad.
I don’t really have any superstitions as such. I try not to anticipate good things too much, but more to avoid to avoid potential disappointment if something goes wrong.
I have a few mostly joky superstitions on related subjects - knocking on wood (I also do the knocking on my head thing if there’s no wood around) or telling people not to tempt fate when talking about good luck or the like. I don’t seriously believe in them, and often don’t bother; it’s more of a vaguely amusing running joke.
I avoid stepping on cracks in the sidewalk. I’m told that the ancient Egyptians had a whole series of days in their calendar, when the stayed indoors and did NOTHING…anybody know of any MODERN superstitions like this?