The simplest machine of all is a lever and a fulcrum, like a see-saw. As you move the fulcrum (the pivot) away from the center of the lever (the platform) you will learn that you can lift a greater and greater weight (albeit a shorter distance) with the same amount of effort. There are a lot of possibilities with a lever.
I found a page on the Rice University web site that has several simple machine projects. URL is below.