The New American magazine publishes the best index on key congressional votes measured against constitutional interpretation, the Freedom Index. They score Congress on key votes every 6 months or so on a percentage basis (0-100). Other "conservative" indexes are weaker tests. They don't view it through a constitutional lens, or if they do, they view it in light of: Implied Powers or "General Welfare" or the Commerce clause or supremacy clause or treaty law or "people have a right to (insert the want)." They may also just consider something 'conservative' if it was proposed by a GOP member and has wide GOP support.
In the 112th Congress, Rand Paul has a score of 93 through the first 30 key votes as measured against the constitutionality of the bills. He is the only Senator with a score above 90. This is for votes through May 2012 in the 112th Congress. Other Senators who scored well: Lee - Utah, Toomey - Penn, DeMint - SCar, and Ron Johnson. Lee had a 87, the others had an 80. If you are curious where we can help Johnson be better by contacting his office and staff and sharing information, he should be pushed on civil rights (he voted for NDAA, extension of Patriot Act), his war stances/foreign policy, as well as "repeal and replace."
In the House there were 9 congressmen with a score of 90 or higher. Ron Paul with 100, Jones (NC) a 97, Duncan (SC), McClintock (CA), Broun (GA), Labrador (ID), Amash (MI) - all had 93, and finally Akin (MO) and Landry (LA) had 90. Of the 5 GOP congressman from WI, the best ranked was Sensenbrenner with 86. Paul Ryan was 4th best of the 5 Republicans with 67, narrowly beating Duffy at 66 for lowest performing GOP congressman in WI through the first 30 key votes.
These scores move around of course dependent on legislation, but there are some consistently at the top. If we get a few more elected who will consistently vote in the 80's or 90s and through time and grass roots effort of professional contacts (email, phone call, letter) to offices of our existing legislators, perhaps those scroring in the 70s, become scores in the 80s, and so forth. On legislation that is close, it doesn't take 250 liberty lovers. It takes a few dozen to swing it to the side of enriched freedom. I just wanted to highlight some folks, who are not perfect, but who consistently get a lot more right than wrong.