** From Andrei Herasimchuk of Involution Studios, a thoroughly detailed chart of various prototyping tools with a criteria breakdown for when to use which tool for which kind of product (web, RIA, kiosk, mobile, etc.) you are designing for:
http://make.involutionstudios.com/conceptcar/
** From Dave Cronin of Cooper, a superb article summarizing various prototyping approaches, with linked resources and citations as well as examples from Adobe Fireworks:
http://www.adobe.com/devnet/fireworks/articles/cooper_prototyping.html
** And from me (ha!) I created a short poster last summer, briefly illustrating a “spectrum of prototyping”, from play to proposal to specification, which is described in this post here.