I have used 3×5 cards and cork board before, but switched to sticky notes on panels of 20×30 foamcore board. These are portable and store easily. I like to code the sticky notes by color, tagged to the P.O.V. (Point-Of-View) character for each chapter or scene.
I’m now in the process of porting this over to Scrivener to see how the virtual environment works for me. Since I tend to do my writing in coffee shops and libraries, I have a feeling the virtual cork board is going to be a better tool for me.