Here's the list of Conan appearances from Wikipedia and Epguides. It seems complete but I could be wrong.
July 25, 2000 - Harrison Ford, Caroline Rhea, North Mississippi Allstars
July 17, 2002 - Harrison Ford, Jennifer Esposito, Wilco
June 13, 2003 - Harrison Ford, Kelly Clarkson, John Pizzarelli
February 7, 2006 - Harrison Ford, Amy Adams, KT Tunstall
May 21, 2008 - Harrison Ford, Eric McCormack & Atmosphere
November 16, 2010 - Harrison Ford, Rosario Dawson, Reggie Watts
August 1, 2011 - Harrison Ford, Marisa Miller, Pitbull
August 15, 2013 - Harrison Ford, Donald Faison, Kurt Braunohler
December 17, 2015 - The Cast of Star Wars: The Force Awakens