Rachel Andrew covered the CSS Grid Layout module in her little CSS3 Layout Modules book (it’s well worth your time and money.) Since there’s been a new working draft published, Rachel has updated her articles. (This is yet another reason I need to get Windows 8 installed somewhere.)
A nifty “flexbox playground and code generator” by Bristol’s Pete Boere.
Chris Mills has recently been doing an incredible job of explaining Flexbox and his article has simple explanations of Flexbox concepts along with practical examples and up-to-date, cross-browser code.