Run by the Centers for Disease Control (CDC) the NCHS collects health information which includes things outside of typical health topics. Additional information includes: mortality & natality, exercise, marriage, injury, and access to health care
Wonderful and overarching datasets in the following sectors:
Agriculture, climate, consumer, education, energy, finance, geospatial, global development, health, jobs & skills, public safety, science & research, weather, business, cities, counties, ethics, law, manufacturing, oceans, states
Statista.com is a statistics portal that integrates data on over 80,000 topics from over 18,000 sources onto a single platform. Categorized into 21 market sectors, Statista.com provides companies, business customers, research institutions, and the academic community with direct access to quantitative data on media, business, finance, politics, and a wide variety of other areas of interest or markets.
Polling is used in a variety of disciplines, and perhaps most heavily in politics. Therefore it is very important to know how to interpret polling results and how a poll is conducted. The National Council on Public Polls has a guide that is "designed to help working journalists do a thorough, professional job covering polls. It is not a primer on how to conduct a public opinion survey." This guide is also very useful for students in interpreting polling results as presented in news articles: 20 Questions A Journalist Should Ask About Poll Results