they're great because they not only provide a template for cutting a perfect circle, but they remain on the head and prevent any tearing, etc. of the drum head.
I second some sort of template. The Holz Snapperz also work very well.
Other than that I've heard of people using a cup or can or something and an exacto knife. This can be tricky though as it is very easy to slip off target while your cutting.
...Other than that I've heard of people using a cup or can or something and an exacto knife. This can be tricky though as it is very easy to slip off target while your cutting.