The National Journal's Congressional rankings for 2005. Rating senators and reps based on their vote history, Alabama's Sessions and Arizona's Ted Franks are the most conservative members of Congress, and Ted Kennedy and California's Pete Stark are the most liberal.
From New Hampshire, Charlie Bass—45.5% liberal, 54.5% conservative, Jeb Bradley—39.2% lib, 60.8% con, Judd Gregg—41.5% v. 58.5%, Sununu—47.2% v. 52.8%.
This rating system has to be seriously screwed up, though—Joe Lieberman is, according to this, 65.7% liberal. There's no way that can be right. A Gore-Lieberman campaign button isn't 65.7% liberal.