"Magic Circle" is kind of a fun treatment - for those of you who haven't tried it before. But, it's easy to become obsessed (there is a HUGE group at Flickr dedicated to Magic Circles - and man, what they can do!)
This is the simplified version. Take any image (this happens to be a Phart to start, but any image with colors works great.) Run
Distortion > Polar Coordinates > "Polar to Rectangle". Click OK. Then run
Distortion > Polar Coordinates > "Rectangle to Polar" > select "Color" (personally, I like Black, but you can pick up any color in your image.) Click OK. Finally, go to resize and choose a Square ratio (1.00 600 x 600 or whatever.) I used PSP9, but Photoshop has the same features to use. Have fun!