"The Bipartisan Policy Center (BPC) drives principled solutions through rigorous analysis, reasoned negotiation, and respectful dialogue. Founded in 2007 by former Senate Majority Leaders Howard Baker, Tom Daschle, Bob Dole and George Mitchell, BPC combines politically-balanced policymaking with strong, proactive advocacy and outreach." - Website
Brendan Nyhan's Blog (with links to his NYT's column "The Upshot")
Monkey Cage (The Washington Post)
Princeton Election Consortium: a first draft of election history
Etalkinghead's Political Blog Directory
This directory groups blogs in broad categories, i.e. Conservative, Liberal, Moderate, Religious.....
Another directory that groups blogs by political or social descriptors.