Data Visualization Guide - From the University of Texas Libraries, this guide is particularly useful for the process of cleaning data before turning it into a visualization.
Core Principles of Data Visualization - This site focuses on how to effectively and clearly present data via visualizations, and features numerous infographics.
Google Public Data Explorer - This site uses public data from a range of international organizations and academic institutions to create visualizations that can be viewed as bar or line graphs, cross sectional plots, or on maps.
Artnome - This site features open datasets from some of the world's most well-known art museums, including MoMA and Tate.
FiveThirtyEight Data - This site provides access to the data behind the articles published in FiveThirtyEight. A wide range of topics are covered but much of it focuses on political polls and sports.
United States Census Bureau - Utilizing statistics from the census, this federal website provides demographic data in a variety of formats and enables different ways of searching.
How's My Waterway? - This Environmental Protection Agency site provides data on water pollutants for the US at large, but can be narrowed by zip code.
Open NASA - Providing access to datasets compiled by NASA, this site also includes open access code and APIs.
50 Best Open Data Sources - This article gathers together 50 open access sites that provide datasets for study and visualization. Categories of datasets include: marketing and social media; academic data; and crime and drug data, among others.
Big Data - From Forbes, this list of 33 open datasets covers topics ranging from Facebook to Amazon to The New York Times.
Open Data Institute: Data as Culture - This site provides access to artwork based on datasets, commissioned by the Open Data Institute.
Deep Dream Generator - This website combines human and artificial intelligence via a neural network to find and enhance patterns in images to create hallucinatory, over-processed images.