Points to Circle is a kewl Cinema 4D script that makes life a lot easier when you're trying to a) create a circle on a polygon object and b) not pull out your hair. It's primarily meant for flat objects but I've had success using it on a sphere. Remember, it's a script, not a plug-in, so look for it under the Script tab once it's downloaded into Cinema 4D. It was written by David Wickenden; a shout-out to 3DKiwi at C4D Cafe for posting it.
You can download it for free here:
Mostly, he writes for a living.