If you can swing it, go for the MP-E macro from Canon F1.4 and will do anywhere between 1x to 5x real life zoom (5x will fill at 35mm frame with a grain of rice from 1 foot, and will focus as close as 1 inch). They only run, oh, about a million and a half bucks!!! No, they are expensive though, really expensive, but probably worth every friggin penny.
Also, and I don't know for sure, but I am looking... You might be able to get an inverter ring for a Canon (I know you can for a nikon). It will allow you to invert a zoom lens, and use it as a macro. The only problem is you will have to find and all manual lens. That should be hard, because it can be any mount, since it would be inverted anyways...
If you find this^ let me know what make it is, so I can get one too. ANd if I find it, I'll leave a little note here
B5