InfoGuides: Data Visualization: Refine Your Visualization

Refining a Visualization

Practical Rules for Using Color in Charts (Stephen Few, Perceptual Edge)
Being Clever with Color website + video (Cole Nussbaumer Knaflic)
Data Looks Better Naked (Dark Horse Analytics) Animated demonstrations that show simplifying chart colors and elements is best.
Telling the Truth (IDV Solutions) - Evaluating the different methods of coloring chloropleth maps, but useful for any categorization of numeric values

ColorBrewer - Assistance picking a color scheme (Cynthia Brewer, Penn State University)
Your Friendly Guide to Colors in Data Visualization - An exploration of color (Lisa Charlotte Rost)

Mistaken Data from Flowing Data (see also Ugly Charts which cannot be fixed)
Makeovers from Storytelling with Data - Includes Excel files with the revised graphs
Makeovers from Stephanie Evergreen - Includes both chart and slide redesigns
Redesigns from PolicyViz - Includes Excel files with the revised graphs
Junk Charts from Kaiser Fung - A huge collection of examples with examples from the news
Chart Busters from Peltier Tech - Many examples with a discussion of various possibilities and reasons
Makeover Mondays - Collaboration between VizWiz and TriMyData
- Provides the Datasets ahead of time; uses Tableau

How to display data badly is a classic article by Howard Wainer in The American Statistician that shows many examples from the scientific literature.
The top ten worst graphs in the scientific literature according to Karl Broman