Robin Good: If you like to go back to pen and paper to draw your sketches, rather than launching the latest web prototyping tool, you are probably still doing the best thing.
As Milos Nedved writes on 1stwebdesigner: "...analog methods of prototyping are especially valuable right at the beginning of projects – when speed matters the most.
Working with paper, or perhaps a whiteboard, can accelerate the speed of our learning loops.
Sketch, feedback, sketch, feedback, sketch feedback – you can go through dozens of iterations in one day and you’ll set solid foundations for the rest of the work.
Consider it kind of premium insurance. Getting rough feedback quickly can save you a lot of work."
The article contains a short review of a set of analog, paper-based, web design/ mobile prototyping tools.