Disjunctivism: In normal cases, when a person is perceiving something, the object of their perception is a mind-independent object. The character of the person's phenomenal experience is explained by the properties of the object (for instance, a person perceiving an apple has an experience of redness because the object of their perception -- the apple -- is red). However, when a person is hallucinating or experiencing an illusion, the object of their perception is some sort of mind-dependent entity (perhaps sense-data; see below). So hallucination and veridical perception are substantially different kinds of mental processes.

Representationalism: Perceptual experience is representational. It represents our immediate environment as being a certain way. Since representations can be both accurate and inaccurate, we can understand both veridical perception and hallucination as the same kind of process. The difference is merely in the success of the representation. To be perceiving is to be representing one's immediate environment in certain ways (visually, aurally, etc.), and perception is accurate to the extent that this representation corresponds to reality.

Sense-datum theory: The objects of our perception are not mind-independent entities, they are mind-dependent objects called sense-data. These are objects like "a red spot at such-and-such position in my visual field". We infer the existence of mind-independent objects from patterns in the sense-data we perceive.

Qualia theory: [I don't think I fully understand the claims of qualia theory. I have tried to describe the kinds of things qualia theorists say, but if it appears confused that's because I am confused.] The phenomenal character of our perceptual experience (the particular way our experience feels) is non-representational. We don't infer information about the external world from the particular feel of our conscious experience; rather, our conscious experience is simply what it feels like (from the inside) to be obtaining sensory information about our environment. One way to put is that my conscious experience doesn't tell me that the apple I'm perceiving is red. My conscious experience is just an effect of the particular way in which I am obtaining information about the apple; I am perceiving the apple red-ly.