Gallup polls individuals about various topics and reports what they find. Many of their polls are public opinion polls. A few are listed below. Gallup's main site is the top link.
Alongside other research, the Pew Research Center uses public opinion polls to glean data on "the issues, attitudes and trends shaping America and the world" ("About" 2016). The link below is Pew Research Center's homepage.
Nielsen Ratings are based on consumer (public opinion) polls and ratings. They rate everything from television shows to condiments. The link is Nielsen's main site.
These are other polling groups or organizations.