An ExtremeHour technique:

''Writing the UserStories on two large sheets of paper was easy, but manipulating the result was a maintenance hassle (kind of like real life). Next time bring a stack of 6 by 18 inch strips of Bristol Board, and write each story on one. Then sort the stack by customer priority, chop it into two iterations, and sort each one by risk. -- PCP''

Bristol Board is light cardboard with a surface good for drawing or writing. It is heavy enough that good-sized sheets (like the 6 by 18 strips above) can be handled without them curling up as paper would. -- RobertField