thoughtbot mixin library http://bourbon.io
thoughtbot responsive grid framework http://neat.bourbon.io
thoughtbot base styles http://bitters.bourbon.io/
thoughtbot patterns and components http://refills.bourbon.io/
thoughtbot style guide https://github.com/thoughtbot/guides (in particular, the Style section)
atomic commits in git http://www.freshconsulting.com/atomic-commits/
getting started with sass http://alistapart.com/article/getting-started-with-sass
sass mixins and a good explanation of placeholder selectors http://alistapart.com/article/dry-ing-out-your-sass-mixins
advanced sass: control directives http://12devs.co.uk/articles/handy-advanced-sass/ (these are used for the studybit icons)