Juli Lynne Charlot. The super fun blog Here's Looking Like You, Kid has a nice couple of postings on the history of circle skirts.
Want to make one? Here is a decent tutorial on the Madame X website. The Whirling Turban website also has a nice description of the different kinds of circle skirts and how they lay on your body. While you are there, be sure to check out their delicious repro dresses.
Of course, if you have a nice full circle skirt, you need a petticoat or crinoline to go with it. Otherwise how will you achieve the oh-so sassy look on the right? The woman in the pictures is Alice Lon and she worked on Lawrence Welk (one of my favorite TV shows when I was a kid). She had an article in T/V. Guide in 1956 explaining how her mother made them. Pettipond.com has recreated the article here.
Both pictures taken from pettipond.com