Paper Prototyping Tips
Five Paper Prototyping Tips
http://www.uie.com/articles/prototyping_tips/
paperprototyping.com
http://www.paperprototyping.com/
User Centered Design and Prototyping
http://pages.cpsc.ucalgary.ca/~sheelagh/courses/481/3users/involve.html
Results from a survey of web prototyping tools usage
http://www.guuui.com/issues/01_03_02.php