Mine was the wire from the oil sensor. I *know* wires don't leak oil (just smoke), so I looked at the oil pan, the valve cover, the oil filter, etc. I wiped them off, drove around, checked them again. Nada. I still had the occasional spots. The next time I changed the oil filter I hit the wire and it fell out- and some oil dropped into the spots.
BTW, if I have a car over ten years old AND it only had a couple dime sized spots after a week I'd be happy.
BTW2, check to see if any oil was dripped at the oil filler hole at the oil change. This is a very common occurance.