It’s Alive: Prototyping in the Browser
Good article about rapid-prototyping websites, includes links to some very useful tools like Sass, Serve, and Susy.
Not mentioned but also extremely useful for local web design: LiveReload and CodeKit, both of which will dynamically compile/process your Sass, Less, CoffeeScript, etc. code AND live-refresh your browser window, every time you save changes to your working files. Why hit the refresh button a million times a day?