Polls tend to vary widely in their numbers depending on how they are conducted.
Politico Polling Center has links to all the major polls with issue search forms.
RealClear Politics does helpful averages of major polls together. The editorial material surrounding it has a decidely conservative slant.
Pew Research Center for the People & the Press "The Center is an independent opinion research group that studies attitudes toward the press, politics and public policy issues. We are best known for regular national surveys that measure public attentiveness to major news stories, and for our polling that charts trends in values and fundamental political and social attitudes."
Quinnipiac University Poll Frequently cited source of political polling data
NY Times The Upshot Who's Winning the Presidential Campaign? "The better guide to who’s really winning is known as the “invisible primary,” in which candidates compete for support from their fellow politicians, from party leaders and from donors."