Cheap extension tube test
So I got bored and ordered this very cheap macro extension tube from DealExtreme. It works, albeit the result is nothing near what you'd get from a dedicated macro lens. It produces noticeable distortion and chromatic aberration, and also turns your EF or EF-S lens into a fixed aperture, manual focus lens. But for less than $10, shipping included, I can't really complain.
Large picture is a 58mm Canon lens cap, taken with the EF 50mm f/1.4 at f/4. Inset shows the tube installed on the camera.