Some believe HAARP caused Sandy
I'm a little surprised (and frankly a little disappointed) to see so few conspiracy theories springing up in the wake of Hurricane Sandy. But one theory that crops up over and over is the idea that Sandy was created by the secret ability of governments to control the weather. Either accidentally or deliberately creating a superstorm.
The HAARP antenna array bears a lot of the brunt of this sort of thing. HAARP has long been a darling of the conspiracy theory set, due to its seemingly mysterious nature and a lot of overheated conjecture. (After watching the Jesse Ventura episode about HAARP, I came to the conclusion that HAARP theories largely boil down to people not understanding what science is or how it works, and a sort of generalized anxiety about government security.)
Chemtrails are showing up in Sandy chatter, too. Under normal circumstances, a passing jet airplane will leave behind a trail of condensation in the sky. These white trails may linger for minutes, even hours after the plane passes, depending on the high altitude weather conditions.
But some claim that these are more than mere condensation trails: they are crop dusting us with chemicals, or seeding the upper atmosphere with (depending on the flavor of theory) chemicals to cause climate change, or particles to reflect sunlight and prevent climate change.
Certainly these jet trails are commonly seen in the sky above New York City and lower Manhattan. It is, after all, one of the world's busiest skies. At times, the aviation traffic is as bad as the vehicular traffic below.
Conspiracy theorists on both sides of the aisle are pointing to Sandy's timing as evidence that it was deliberate. Those on the left believe that Republicans created Sandy in order to make Obama look bad, and to disrupt the ability of liberal and non-white New Yorkers to get to their polling places. Those on the right believe that Obama engineered Sandy to force Americans to rely on his good will, thus engendering positive feelings towards the incumbent that would translate to votes.
(Neither side can account for the fact that Romney has openly advocated dismantling FEMA in the past. Even Republicans are disowning him on that point right now.)
And on the other hand, you have those who believe that Sandy is the result of climate tinkering gone out of control. I suppose for some people it's easier to believe that the government is to blame for a disaster of this magnitude, than that the world's climate is changing for the worst.