The Functional Art – Alberto Cairo.
The best I’ve read on designing data visualisations and infographics, and which I constantly refer back to.
Design for Information – Isabel Meirelles
Really good theory and explanation about how and why visualisations work.
http://www.edwardtufte.com/tufte/books_vdqi
This is where I started:
http://chimera.labs.oreilly.com/books/1230000000345/index.html
and I now use these a lot too:
https://leanpub.com/D3-Tips-and-Tricks
https://www.dashingd3js.com/ (for the newsletter mainly)
The forums on Stackoverflow (http://stackoverflow.com/questions/tagged/d3.js) and Google Groups are super useful (https://groups.google.com/forum/#!forum/d3-js).
If you are practicing on your own PC at home, then you need to run a local server; I use the node.js http-server on my laptop:
http://www.jhh.me/blog/2012/12/24/setting-up-http-server-on-windows-with-node-js/
https://github.com/mbostock/d3/wiki/Gallery
http://christopheviau.com/d3list/gallery.html
http://www.thefunctionalart.com/
http://junkcharts.typepad.com/junk_charts/
http://www.informationisbeautifulawards.com/
http://www.informationisbeautiful.net/
http://square.github.io/crossfilter/ - allows you to reduce/group data (aka like PivotTables in Excel but in code) in your javascript\
http://nickqizhu.github.io/dc.js/ - allows you to easily create linked charts (nb requires crossfilter as well)
https://github.com/d3/d3-plugins/tree/master/sankey - extends D3.js to make Sankey diagrams
http://dimplejs.org/ and http://nvd3.org/ provides a simpler library for creating standard charts using D3.js
http://raw.densitydesign.org - provides a GUI into more sophisticated D3 visualisations