I find I spend a lot of time here discussing less than stellar information visualizations and how they can be improved. But there is also much to be learned about data viz best practices by examining good visuals and understanding why they are effective. I paused on one such graphic last week (see original article):

Here's a quick rundown of what I like about the above visual:

Everything is labeled (titles, axes, important values, data source), so there's no question about what you're looking at. The overall title explains what the visuals are intended to convince you of (so there's no guessing!). The points they want to highlight (2011) are shown clearly and draw attention through use of color-heavy call out boxes.
The use of color is intentional (not what a graphing application randomly chose); note how red means the same thing in both graphs: total. This consistency is important for easy comprehension.
There isn't any extraneous stuff to dilute the audience's attention. Everything that's there is adding informative value.
The visual hierarchy of information is clear. The data draws your attention through color; titles are bold so you can't help but know what you're looking at. Axis labels are less emphasized (but still clearly legible) with non-bold font. Sources and gridlines are there to help interpret the data, but are pushed to the background through size and weight so they don't compete visually with the data.
Perhaps most importantly, the visual fits well with the article it accompanies. The graphs reinforce the main takeaways from the article and vice versa.

WSJ in general tends to have effective data representations, so if you're looking for more good examples, this is a great source. I still encourage you to maintain a critical eye when looking at any data visualization: observe what works well and what doesn't and try to emulate the effective parts in your own visuals.

Do you have any favorite sources for good data viz?