2017
2017-07: Top 10 Free Drupal Themes (vardot.com).
2015
Be inspired by this search on Drupal.org.
Bootstrap - On GrN.dk i currently am trying out a simple, mobile friendly, generic, responsive theme with only minor adjustments. The thing that is a bit annoying is the Bootstrap CDN that claims it gives faster load times. In my case it actually increases the load time of the page - at least here in Denmark where my primary focus currently is. Any thoughts on this?
Gratis - Pretty slick out of the box responsive theme with great color options. I am using it on a couple of web sites: HelePlanter.dk, GoNude.dk and StegtFlaeskMedPersillesovs.dk
Zurb Foundation - came across this theme project which sounds very good and has been recommended by some people for ecommerce setup.
Omega Kickstart - a theme designed for the Drupal Commerce Kickstart installation. Will probably try this out for my upcoming web shop - ecommerce project. Yes, I use it now at Underhyleren.dk - sales of cheap but good quality boxershorts in the Nordics.