These resources are mostly statistical, at the moment. Please add some for big data!
AnIntroductionToStatisticalLearning
TheElementsOfStatisticalLearning
NistSematechHandbookOfStatisticalMethods
TheShapeOfData: https://shapeofdata.wordpress.com/
WinVector: http://www.win-vector.com/blog/
EvanMiller: http://www.evanmiller.org/
JohnCook: http://www.johndcook.com/blog/
StatisticsBlog: http://www.statisticsblog.com/
ChrisStucchio: https://www.chrisstucchio.com/
RBloggers: https://www.r-bloggers.com/
DataTau: http://www.datatau.com/
KDnuggets: http://www.kdnuggets.com/