Yesterday I discovered a migic little for making mobile-friendly sites, its the viewport meta tag. It goes something like this:
<meta name="viewport" content="width=device-width, initial-scale=1.0, user-scalable=yes">
It tells the browser to set the page width to the same size as the targets screen (I am pretty sure it gets mostly ignored on desktop browsers)
This allows you to create variable width pages that will look right on almost any size of screen. Though there are still a few more tricks to perform to make everything look right all of the time. Head on over to HTML5 Rocks for more info.