Gerald Posner's "Case Closed" is the best anti-conspiracy book there is, and should be read by everyone who subscribes to any of the popular (or unpopular) conspiracy theories, because he blows holes in many of the common assertions about the case -- Oswald wasn't a good enough marksman, the rifle couldn't be fired that rapidly, an unusual number of people associated with the case died early deaths, etc. -- none of which assertions are true.
Doesn't mean he's right, but it DOES mean that a lot of conspiracy "evidence" is rubbish. But not all of it.
The assassination is such a complex, swirling swamp of craziness and conflicting testimony, almost all of it misremembered or hiding secret agendas that it makes"Rashomon" look like an arithmetic problem. It's easy to get lost in it yourself. Posner can help you keep your bearings even if you decide you disagree with him.
To my mind, it's pretty definite that Oswald did it and did it alone. I think he was perfect for the crime, and I also think that no one in their right mind would have conspired with him for more than five seconds. One also has to consider that the usual suspects are about as competent as the Watergate burglars a decade later (some will tell you they're the same guys), and there is no way in hell those guys could have covered up a prank phone call, let alone the murder of a president for sixty years.