I’m surprised nobody started a thread like this so far.
http://www.nytimes.com/-Your standard newspaper of record
http://www.washingtonpost.com/-A very good paper for politics, I like their opinions in general better than the NYT
http://www.politico.com/-More political news
http://www.realclearpolitics.com/-Good roundup of political news from all over the web
http://www.theatlantic.com/-Excellent periodical with some good in-depth articles
http://www.nationalreview.com/-Get your fill of conservative commentary
http://www.tnr.com/-Ditto for liberal commentary
And two of my personal favourites:
http://american.com/-Very well thought out opinion pieces on often obscure issues
http://welections.wordpress.com/-Possibly the most awesome blog ever IMO. Analyzes major elections from around the world from America to Ghana including background, electoral geography, and voting trends.