Circles : Antique Buttons on a Wooden Stump
Old Buttons on Old Wood
Plus the growth rings from the tree adds yet another layer of circles.
Concrete Culverts from a Construction Site
I was also thinking about rain drops falling, and the circles the ripples make from the drops.
Circles in Motion.
Not a great image (It's tricky to shoot in the rain), but something to work on for the future.
Or even video.