Erin Babnick's article on color theory - Erin has a tonne of great articles that I would definitely recommend but I found this one the most useful.
Ted Gore's free post processing tutorial - A great tutorial on how to process a sand dune shot. Ted also has an excellent blog post on color theory on his website.
Adam Gibbs youtube channel - Full of many great informative videos on a wide range of topics from processing to composition.
Enrico Fossati photography
Alex Noriega photography
Marc Adamus photography
Guy Tal photography
Erin Babnik photography
Matt Jackish photography