Another set of *very* useful tools for responsive HTML design, in addition to custom drop down menus, pagination, typography, etc. is the Twitter Bootstrap suite of tools. I use it, along with JQuery and Fancybox to create responsive sites (example: http://www.hgnlive.com), and I am extremely impressed with the flexibility of the tools.

The Twitter Bootstrap tools can be found at http://twitter.github.com/bootstrap/