A great visualisation relies on interesting, topical and informative data, so here are a few sources I work with. visualizing.org is an excellent data viz community site that compiles and releases open data sets relevant to today’s pressing issues.
The Guardian Data Blog is an excellent resource for topical datasets, and their interactive visualisations are a good place for inspiration while you're there.
Ipsos MORI is one of the leading political, social and business research companies in the UK and Ireland, and they have a large amount of publically available data in their research archive.
The United Nations' Development Programme, is an organization advocating for change and connecting countries to knowledge, experience and resources to help people build a better life. The UNDP's data sets are publically available and extensive
Tributary is an experimental environment, specifically for rapidly prototyping visualization code.
The tutorials on this site need you to know a bit about HTML and CSS, as well as some JS. If you're starting from scratch in any or all of these languages there are thousands of options available to you but I recommend Code Academy highest of all because its interactive and enjoyable.
If you want to read rather than do exercises then Shay Howe's Learn HTML and CSS is a great place to start and when you're done you can follow it on to the next level with the elegant Learn CSS Layout tutorial.
SVG stands for scaleable vector graphics. It is an image type for the web that can be rescaled to any size and maintain its quality and because it is an XML markup element in itself its file size is minimal in comparison to bitmap imagery. SVG is used widely throughout data visualisation online due to its ability to be animated and manipulated to become interactive.
Enjalot, the creator of Tributary, has a number of d3 tutorial videos online at dot enter covering d3 colour scales, basic d3 circles, d3 path, simple d3 transition and d3 stacked bars. He also has the sister site dot append covering d3 drag behaviour, d3 brush, crossfilter and reusable bar charts. I do find some of them hard to follow because of the background music but they are a useful resource..
My favourite data viz blog is The Why Axis, edited by Bryan Connor, which documents the rise of data visualization in the digital age.
Andy Kirk is a UK-based freelance data visualisation consultant, trainer, author, speaker, researcher and editor of visualisingdata.com. It provides readers with a variety of content that charts the development of the data visualisation field.
There are many different online data visualisation tools available but these are the ones I intend to cover on this site.