Really? Huffington Post is the most leftist/socialist site on the planet? Maybe in the eyes of Fox News viewers. Arianna Huffington herself (http://en.wikipedia.org/wiki/Arianna_Huffington) is very, very far from being affiliated with socialism.
Here are a few (well worth reading) sites that are actually closer to your description:
Huffington Post likes to post headlines and blog posts praising all things green energy, Obama, and NBC. The bias is pretty obvious. The original point of the site was to be a left-wing alternative to Drudge Report--even the name is a play off of it. Ariana Huffington herself has spoken at several Democrat events over the years and is considered politically left-of-center.
Here are a few (well worth reading) sites that are actually closer to your description:
http://www.zcommunications.org/znet
http://monthlyreview.org/
http://links.org.au/