Hobson's choice (Words Formerly Known As Proper Names):

Caesarean section (after Julius Caesar)
dunce (after John Duns Scotus)
Hobson's choice (after Thomas Hobson)
John Hancock (after John Hancock)
John Henry (after John Henry)
keeshond (after a nickname for Cornelius) [contributed by Edge]
Kelvin (after William Thomson, Lord Kelvin) [contributed by Edge]
Kemp's ridley (after Richard M. Kemp) [contributed by Edge]
Keogh plan (after Eugene James Keogh) [contributed by Edge]
Lippes loop (after Jack Lippes) [contributed by Edge]
Melba sauce and Melba toast (after Nellie Melba)
sideburns (after Ambrose Burnside)

Please email me with more examples of these (contributions will be posted): anotherjerryhill@angelfire.com