Templated is a collection of over 800+ simple CSS, HTML5 & responsive website templates, built and released for free under the Creative Commons.
Colorlib offers some of the best free WordPress themes, responsive and full of options, ranging from business themes to blogs and portfolios.
Share bootstrap offers great free themes and templates built with Bootstrap. It is an especially great resource for Dashboard templates and themes.
Just Free Themes offer over 1,000+ awesome, pixel perfect and free WordPress Themes, ranging from eCommerce to blogging to fashion and more.