The official Senate website of Senator Bernie Sanders (Ind.-VT) links to a comprehensive list of people who have been elected or re-elected to the Senate or House of Representatives as Independents :http://www.sanders.senate.gov/download/independent-members-of-congress?inline=file
The list includes members who were always Independent, along with Senators or Congressmen who were elected on a party ticket and later were re-elected as Independents. Each name is a live link to the profile of the member @ the Biographical Dictionary of the United States Congress.
Senator Sanders apparently posted the list in order to validate his claim to be the longest-serving Independent in Congress. Bernie Sanders was elected to the House of Representatives in 1990, and re-elected every two years until 2006, when he was elected to the United States Senate. Senator Sanders was re-elected in 2012 and will be up for re-election in 2018.
The list also shows that Independents have been far more successful in elections for the U.S. Congress than in any campaign for President. Useful intellectual ammunition for people involved in alternative politics.
Ironically, I found this link in the profile of Sen. Sanders on the website of the Vermont Democratic Party, which supported Bernie Sanders in his election to the U.S. Senate in 2006 and his re-election bid in 2012.