I am an unabashed fan of conspiracy theories. That doesn't mean I believe them--I believe alarmingly few, actually--but I am fascinated by them nonetheless. They help explain the unexplained. confirm our worst fears, and--probably most important--make us think we know something the rest of the population doesn't.
If you're into that sort of thing, the baseline is Coast to Coast AM. While they don't deal exclusively with conspiracy theories (they have a lot of alien stuff they run into the ground and childish paranormal stuff that doesn't interest me in the least) most likely if it's a valid or well-known conspiracy, they've addressed it in some manner.
Still, not every conspiracy theory is valid. E-mail chains to the contrary, most conspiracies don't have legs. The initial maelstrom of confusion during an event forces people to come up with alternate ideas to fill in the gap, but as the truth becomes known the conspiracy slips away into nothing.
Musing about this earlier today, I formed a theory of conspiracy theories. I'm sure this is nothing new, but even amongst the crackpots there's a certain level of credulity that's required. Placing faith in an obvious lie does you no good if you're peddling twenty other "truths" that can be legitimately discussed. So what makes a good conspiracy theory?
1. It fills an insatiable need for an answer that doesn't exist. No one propagates theories about stuff no one really cares about. You may have people who believe their pet theory may seem obscure but ripples throughout the world in important waves, but by and large most people won't waste the time. But don't let that fool you--what may seem small (water fluoridation) may end up having large impacts (those damn Reds are poisoning us!)
2. There has to be a reason for a conspiracy. There has to be a question as to why the information that is verifiable doesn't answer all the questions, or does not provide sufficient motive for the actors. Kennedy being assassinated is a tragedy, but inconclusive evidence of the actual shooting, along with the Kennedy family's unusually dense network of conspiracy-laden agents (read: New England elites, European connections, and a growing communist menace) and Oswald's ill-timed demise, raised too many questions that empirical evidence could never prove.
3. There has to be a plausible (if unlikely) non-conspiratorial explanation. In order for a conspiracy to resonate with people, it has to have a certain level of doubt. If the theory is so outlandish that there can't be an alternate explanation--even one with a remote chance--no one will believe it. A truly effective conspiracy theory has to have an element of denial along with plenty of justifications as to how unlikely the "official" story is. These aren't necessarily contradictory, but actually can enhance each other easily.
Take my personal pet conspiracy theory of the moment--Polybius. Polybius was supposedly an arcade game planted in a few places in the Pacific Northwest in the early 80's that was highly addictive and mimicked sensory psychoactive responses. Players would get sick after playing but couldn't stop. Men in black would come around and collect data; presumably, these were government agents field testing some new method of psychological warfare.
The early days of video games aren't documented all that well, since many assumed they would be a fad, and the industry was new enough that there wasn't a trade publication on the commercial side. So it is plausible that an arcade game was set up and removed quickly with little notice. It's possible that the government experimented with this brand new medium that was already misunderstood by parents, officials, and even the bar owners hosting the games--it's proven governments have done things like this in the past. But it's equally plausible that no such game existed, or that it was a prototype or a failed company and men in suits were there to audit renters to make sure they weren't cheating them out of quarters.
Conspiracy theories, to me, are fun, any many contain alarmingly effective grains of truth in them. But they can also be used as excuses for bad behavior. Still, despite the popularity of things such as The Da Vinci Code, I think this is a rich, untapped cultural mine that has yet to be explored.
At least, that's what they want you to believe.