"The home of the U.S. Government’s open data. Here you will find data, tools, and resources to conduct research, develop web and mobile applications, design data visualizations, and more."
"Similar to how Google Scholar works, Dataset Search lets you find datasets wherever they’re hosted, whether it’s a publisher's site, a digital library, or an author's personal web page. " ~Google
"Dedicated to making high value health data more accessible to entrepreneurs, researchers, and policy makers in the hopes of better health outcomes for all."
"Inside Kaggle you’ll find all the code & data you need to do your data science work. Use over 19,000 public datasets and 200,000 public notebooks to conquer any analysis in no time."
You can find many source datasets associated with research published on ACM. Simply apply the "Artifacts Available" filter under the Reproducibility Badges heading (left side-bar in search results). After that, open an item of interest and check the link under "Related Artifact."
"This database contains 250,000 data maps, hundreds of profile reports, 220 years of demographic data, 40 billion data elements and 500,000 variables."
"Its online database holds more than 500 different variables, covering themes like Freshwater, Population, Forests, Emissions, Climate, Disasters, Health and GDP. "