You might find this SitePoint book useful:
There are also a number of articles about RWD, including these:
http://www.sitepoint.com/web-foundations/what-is-responsive-web-design/
http://www.sitepoint.com/responsive-design-vs-m-sites/
http://www.sitepoint.com/12-essential-responsive-design-tools/
But as Ryan says, it’s not nearly as scary as it sounds once you start to get into it.