We all love infographics: http://designinstruct.com/roundups/infographics-learn-responsive-web-design/
Responsively Retrofitting An Existing Site With RWD Retrofit
Another responsive design resource: http://webflow.com/
This would be good if you know some css but don’t want to write the code from scratch. It’s sort of a WYSIWYG editor online that exports the html and css for you. They have a live demo that you can play with.
Patterns in Responsive Design: http://www.lukew.com/ff/entry.asp?1514
A little more on “Off Canvas” design: http://jasonweaver.name/lab/offcanvas/
An article that sparked many things in 2010: http://alistapart.com/article/responsive-web-design (as many A List Apart articles do).
We use Foundation to prototype all our sites and run drafts by clients: http://foundation.zurb.com/
We use Bones to build out our themes from scratch: http://themble.com/bones/ (do read through his files, best markup of all time).
http://www.browserstack.com/ for testing