I made
this page a while ago for different reasons, but it will work here.
Put in an address or a city, state or some other point google knows about and a mile figure (200, 300, etc.), press "Calc Circle" and give it a few sec. It will draw two circles: A red one which is an absolute miles from your address, and then a green shaded area that that uses directions (it divides the circle up into N parts then ask google for directions so the outer bounds of the green area is actual driving miles).
Here is an example of about 50 miles from Chicago: