There's a lot of stuff on this site. Where to start? Here is a little introduction and a number of pointers to get you started.
Visualization is so fascinating because it's done in so many ways and touches so many other fields: perceptual psychology, statistics, computer graphics, journalism, etc.
I try to cover as much of this variety on this site as I can. It gets difficult to keep track of all the different things though…
What Are We Even Talking About?
While the variety of things that are called visualization are great, they can also get confusing. What's the difference between infographics and visualization?
It's the raw material of data visualization, and there's a lot of confusion around it. Familiarize yourself with the differences between spreadsheet thinking and database thinking, and then learn about how thinking on the level of individual data items is different from thinking in terms of aggregates.
Data journalism has produced some really interesting visualizations recently.
There are lots of different chart types and visualization techniques. Here are a few that I've talked about.
Pie charts are a contentious topic and deserve their own page. There you'll find an overview of how they work, some good and bad examples, and pointers to some research.
I also have a separate page that lists all the articles I've written about different techniques and chart types.
I use criticism in the way it's used in art and design: ask questions, understand, try to improve. I've written about criticism as a tool for doing research, and written a number of critiques (not always in the criticism category).
I have criticized ideas that keep getting taught even though they are not actually meaningful or useful, like Chernoff Faces or the many abuses of the periodic system of elements.
Other topics include questions about the Challenger disaster example that is often taught in visualization courses. Also, the story behind John Snow's Cholera map is different much more interesting than many people think.