[tonycoco]

The Visual Display of Quantitative Information: Edward R. Tufte

Ways to Connect: On Interface and Product Design, Ryan Singer

Something on color theory

Design language books (Bauhaus, etc)

The entire Google design team has quite a few open resources: https://material.io/design/ and https://design.google

[mt3ck]

definitely second Tufte, lots of good info on consolidation and creating coherent charts and maps from large datasets

[xtracto]

I read Tufte during my PhD and it was a lifesaver. It is good in many levels: Not only for the lessons in doing good graphics, but also on the history of charts. (I was surprised by the history of the first scatterplot)