My simple macro setup: a 20D, a 50mm f1.8, a 580EXII, a Gary Fong Lightsphere (this is just about the only use I have for it), and an off-camera shoe cord. The Lightsphere works great for macro applications because it's a relatively large light source, although with such close working distance, the light falls off rather quickly.
My DIY extension tube is great. I glued a body cap and a rear lens cap together and cut out the center. I don't know the exact length, but it's about 17mm or so.
The lens aperture can be manually set by removing the lens from the camera while holding the DOF preview button. (Some people have told me this is a dangerous method, but I haven't had any problems so far.) The camera will display "00" in place of the actual aperture and no aperture data will show up in EXIF.
strobist info: Canon 430EX(bare) handheld camera left, aimed at ceiling.