In his latest novel, author Michael Crichton has a major character who flashes a badge whenever he needs legal authority. The office he works for? The "National Security Intelligence Agency".
So far as I know, the NSIA does not exist as a government entity; Crichton appears to have created the agency purely for his story. But that does not mean there are not more than a dozen agencies, which are largely unknown to the population.
There are fifteen official government agencies which are classed as intelligence agencies. Many more perform intelligence-gathering tasks or analysis, but are not considered intelligence agencies by nature. Then there are the "black" agencies, which are never publically recognized. And that does not go into the private groups, created to perform tasks for foundations and corporations, and also for those tasks the government does not wish to have connections revealed.
Sometime in the next week, I will examine this phenomenon in greater detail.