Update: Layers magazine Tip of the Day 16 Oct 2007 adds 'Spiraling Circles,'
"Here's a cool trick that's the result of a conversation with my friend, GarySped, from the Layers Forum. Click on your Artboard with the Ellipse tool (L) and in the window that opens, make the Width 1.25". Then click on the word "Height" and fill in the same value, and then press OK. With this newly drawn circle still selected, go to Effect > Distort & Transform > Transform. In the window that opens, type in the following specs: 80% for both Horizontal and Vertical Scale; 1.0158" for both Horizontal and Vertical Move; 60 for Rotate Angle; and 25 for the Number of Copies. Now click OK to make the circle spiral. Cool trick Gary!"
Update: see also Ellipse Tool Plus from Hypoly, a preset for After Effects.