Watt - inventor of the steam engine
Fahrenheit - can't remember the guy's name but he was a German scientist
Thomist, Thomism - Thomas Aquinas, medieval doctor of the Catholic Church
Jansenism - after a puritanical French priest who was very influential in the Catholic church; later condemned
Nestorian - Greek bishop condemned by the Catholic church
Arianism - Arius, another early heretic
Mennonite - after Menno Simmons, Anabaptist leader
Amish - after Jacob Amman, Anabaptist leader who broke with Simmons
Marconi - early name for wireless radio
Morse - Samuel Morse
Braille - Louis Braille
Hoover - vacuum cleaner
also, let's not forget Gerrymander, since this is an election year
And one of my favorites, a little obsolete, but fun anyway
Sam Hill (as in what the Sam Hill). There seem to be many versions of the Sam Hill story, but according to Upper Peninsula lore, the original Sam Hill was a surveyor in Michigan's Copper Country who was known for his salty language.