If you are a user of the Canon EOS system and have decided that macro work is something that is worth trying then one lens above all others should be on your must have list. That lens is the MPE65.
Now this is not an easy lens to use. There is no focus other than move the camera closer of further away. It has a very shallow depth of field and needs a flash to freeze any movement from camera shake as well as illuminate the object. In short it can be a real dog to use.
However when one gets used to its difficulties it can do amazing things. I have used it to photograph a wine bottle via the gas bubbles found in champagne (took me two years of on and off trying to get it). Its ability to magnify up to five times yes that is five times provides a view into details most people cannot see or photograph.
A few days ago I found a wasp drowning in my pool, this is the result of using the MPE65 at about 3 times magnification after I put the wasp on a Camelia flower.
Then there is that group of spiders called jumping spiders that have great big eyes out front, they look like this when captured with the lens. This spider is about the size of a grain of rice.