Worth a look at What Is A Conspiracy, which starts with a dictionary definition, and Conspiracy Theory, which starts with an example use of the term. The Myth Of Death Of JFK suggests that this event more than any other triggered the modern interest in the subject.

Possible Conspiracy Theories was drawn up in the earliest days of Why and has some useful Why Humor to leaven the lump.

The award-winning radio show Broadcasting House started its mainly excellent summary of this area on Saturday 26th July 2003:

If you're 100% convinced the photos of Uday and Qusay Hussein are genuine, that there's no doubt that Dr David Kelly committed suicide, and that they got the right man for the assassination of President Kennedy, you're probably in a minority. Chris Ledgard reports on the perennial appeal of the conspiracy theory.

That was three theories in the first sentence. In total I counted nine different theories, mostly using a very simplified Prime Assertion, as constructed by BBC scriptwriters. This suggested the idea of a canonical set of BBC Conspiracies leading to the BBC Conspiracy Test. The Times Conspiracies in the September 2003 article referred to in Borderline Conspiracy Theorist were rather different.

Conspiracy Theories by Robin Ramsay has a review in that page. There are of course lots of other books of the same name. With the help of more splits we should be fine with that. A similar effort just called Conspiracy published last year is worth comparing.

Al Jazeera's extraordinary section of their website aljazeera.com/cgi-bin/conspiracy_theory indicates what the English term means to these key trend-setters and influencers of the Arab world. They don't take the wholly pejorative approach trenchantly put forward by Keith Braithwaite as the only sensible way in Opposite Of Conspiracy Theory, to put it mildly.