As stated on the web site, the goal of FiveThirtyEight is to help New York Times readers make sense of several different topics, politics included, "largely thought statistical means."
This site has become known for its polls focusing on major elections, the presidential election being no exception. It features nation and state poll projections as well other project analysis. This site also includes a list of other helpful resources and a blog.
Gallup is a well respected name in the field. As stated formerly on the web site, "Gallup's reputation for delivering relevant, timely, and visionary research on what people around the world think and feel is the cornerstone of the organization." Be sure to check out their page on the 2016 elections.
Like Gallup, the Pew Center is another big and reliable name in the field. "Pew Research Center is a nonpartisan fact tank that informs the public about the issues, attitudes and trends shaping America and the world. It conducts public opinion polling, demographic research, media content analysis and other empirical social science research." Though the interface tends to change as polls are conducted monthly, the site currently has a section entitled, "Election 2016."
Additionally there is a section devoted to the 2016 elections on the right side of the home page.