I started working on a site recently using the Omega theme. In general, I find (once you get used to its ins and outs) Omega is a great theme to get a responsive Drupal 7 site off the ground relatively quickly. It comes packaged with all sorts of goodies, and is based (and includes) the 960 Grid System. Read more about Drupal 7: Moving the Footer Outside of the Page Wrapper in the Omega Theme