D3GL is under heavy development at the moment, and you can check out the most recent developments at http://github.com/jiwonkim/d3gl.
You can check out the official D3GL site at http://d3gl.org.
Check out D3.js, the library that D3GL builds on top of, at http://d3js.org.
As more data visualization types and primitives are added to D3GL, the list will grow. Existing tutorials will be linked - unlinked tutorials are yet to be written.
In addition to explaining basic D3GL concepts and usages, these tutorials will also discuss the internal implementation of each feature for those who are interested in adding to the open-source development of D3GL.