Tamar Ansh had an interesting article in the Jewish Press in which she demonstrated a technique for making a braided round challah. Basically, what you do is make a three strand braid with a fourth strand going through the center, perpendicular to the braid. Then you pull it into a ball.
I baked most of my round challahs this year in round foil pans. The 7″ is perfect for 1 pound challah, the 8″ is good for 1 1/2 pound loaves, and the bulkeleh pans take about 8 ounces each.