http://www.thenation.com/TNR was founded in 1914.
http://www.tnr.com/TNR hasn't been a flagship magazine of the left in a very long time.
Two other good magazines that I like:
Mother Jones was founded in 1974.
http://www.motherjones.com/I tend to read the American Prospect the most, myself. (founded in 1990):
WHEN YOU'VE LOST THE NEW REPUBLIC . . . Tapped's new favorite thing is the Federal Election Commission database where you can type in anyone's name and see if he or she has donated money to political candidates or parties. (Tapped's old favorite thing was The Washington Post's home buyer database, where you could learn how much your neighbors spent for their apartments.) So check out this nifty little listing (go
here and search for “Steinhardt, Michael”) that we discovered while trying to see which big-shot New Democrats were supporting which Democratic presidential candidates: According to this list, Michael Steinhardt, former Democratc Leadership Council stalwart and part-owner of The New Republic, gave $2,000 to Bush-Cheney '04 Inc. on June 20, 2003.
Now, we know that there's often little direct relationship between a magazine owner's politics and the views of its writers, but it is a notable thing when one of the more prominent New Democrats around starts financing the continuation of the Bush administration.
http://www.prospect.org/weblog/archives/2003/07/index.html#001288