I really dont want to start a flamewar, but wasnt a byproduct of the occupation an upsurge in contracts between Iraqi oil and foreign firms? From what I understand, everyone got a slice of the pie that use to be a nationalized oil industry.
Well, if the allegation was that the Americans invaded for the purpose of giving Iraqi oil to American companies, I don't think that was quite how it played out. Lots of other nations, including ostensible anti-imperialists France and China, saw their oil firms jumping into the feed.
That said, I don't know if making claims about the motivations of a particular action in and of itself qulifies as a conspiracy-theory, even if the claims turn out to be false. Historians debate politicans and governments' motivations all the time, without it being called conspiracy theory.
I think that distinguishes a conspiracy-theory from everyday historical theorizing is that the theorists' allege that the alignment of powers behind the scenes is radically different than what is generally assumed. For example, we might think that it was a bunch of disgruntled southerners who took out Lincoln, but in reality it was THE JESUITS! And we're all dupes for thinking that the Jesuits would never intervene in Americans politicis that way.
Also, they like to claim that certain extraoridinary events have happened that are being kept from the public's knowledge, eg. Roswell.