I’ve been meaning to link to Voteview for a while now. It’s a project of Keith T Poole, now at UCSD, that ranks congressfolk on a liberal-to-conservative scale based on their voting history. There’s lots to browse, but the rankings themselves are as interesting as anything on the site. Check out the 110th Senate, for example, and find John McCain in the 109th Senate rankings (but first, without peeking, guess where he ends up on the scale).
There’s an infrequent blog; the most recent entry is nominally about the political closeness of Clinton and Obama, but goes on provide historical perspective on Congress’s current polarization.