Lighting macro subjects is always tricky - you are so are usually so close to the subject that there is a tendency to shadow some of it with your body / camera kit.
If the subject is in the open and you can get a reasonable distance from it (because it is reasonably large, like a flower, or you have a longer macro lens - say a 180mm) then flash may not be necessary. In many cases flash will be required, especially as you'll probably want a small aperture to increase depth of field.
The problem with some flashes is the dull flat light you get - this is a problem with ring flashes - they might be great for dentists getting evenly lit shots of teeth, but make bug shots look boring. I prefer to use an ordinary flash off camera (I have it on a bracket to the side of my camera and use a mini ball head to angle it as required). A more expensive option is something like the Canon MT-24EX which has two mini flash guns which can be angled independently and powered to different levels to allow some shadows in giving more depth to the shot.