According to http://www.voteview.com out of 3,320 individuals who served in either or both the house and senate from 1937 until 2002 Ron Paul tops the list as most conservative of the bunch. The link to view the list http://www.voteview.com/is_john_kerry_a_liberal.htm
http://www.conservative.org/ratings/ratingsarchive/2010/House-Senate-combo.htm#TX
On The Issues has Paul's voting record as a 'moderate libertarian'.