And how did I forget finishing The Visual Display of Quantitative Information? It's a beautifully designed history and primer-by example of on how to visualize data (the medium is the message; it's a beautiful book), especially useful for scientists, but useful for anyone who wants to use graphics to explore data. You can read more about it here.
The guy who wrote it is Edward Tufte, a pioneer in visualization. He has a website.
I also recently happened across a site called Information Aesthetics, which showcases the creative display of data in the news and on the net. It's fascinating stuff; bookmark it, subscribe to it. Here's an example: the flow of user traffic through various pages on a single web site is visualized as a circle, with heavy lines for the most common pathways through. Sure, they're gorgeous, but they also show how people tend to use the website, which can provide insights to the site designer.
The post title is almost my favorite "visualize X" bumper sticker. One day I thought of one I liked better, and I told Sarah, and it cracked us up. If it doesn't crack you up, you obviously have an impaired humor system and you should get it checked out:
Visualize Using Your Turn Signal