In previous Information Technology classes I've taught, I've brought in an old desktop computer and "dissected" it with the students, which immediately gets them intrigued and wanting to learn more. Sometimes I lead the walkthrough, other times I have a knowledgeable student do it, and others I'll have a group be completely on their own trying to find all the parts.
I really like the comparisons of the components to parts of the human body and tend to emphasize that in instruction. This year I might have students try to act out the parts of the computer as a complete system to complete a simple task, i.e. someone moves and presses a student's head (mouse), which gets another student (CPU) buzzing and commands that the hard drive and RAM start retrieving and storing data, etc.