I have read both books mentioned which are great.
I really like Zurb Foundation. I have built a few sites with it and had no issues. I have found it easy to extend - it's easy to build a prototype that and then take to full production. (I've been using version 2 - there is V3 out - however V3 has dropped support for IE7)
A new tool someone in the office was playing with was jetstrap.com
Let's you visually do responsive layouts - you can then check the code and see how it's done and might be a good way to get started.
