Regularly surveys residents in Colorado, Connecticut, Florida, Iowa, New Jersey, New York, Ohio, Pennsylvania, Virginia and nationwide about political races, state and national elections, and issues of public concern.
Pew Research conducts research on a wide range of topics. In terms of the 2016 general election, they focus on "people’s engagement in the election, opinions about the candidates, views of the campaign and voter preferences."
FiveThirtyEight provides analyzes statistical information to explain and forecast political events. They also provide pollster ratings by assigning a to pollsters, which are calculated by analyzing the historical accuracy of each firm's polls along with its methodology.
RealClearPolitics aggregates polling data and calculates an average of these.
Gallup Polls conducts regular public opinion polls.
HuffPost Pollster tracks thousands of public polls to give you the latest data on elections, political opinions and more.