Joseph Clement Coll, Daniel Vierge -- both golden age of illustration people -- William Heath Robinson. If you have never been to Bud Plant's web page -- he's an OLD Comics Fan who broadened his interest to golden age illustrators and has biographies and samples from an AWESOME variety of people.
I would also say Honore Daumier by the way. I respect Thomas Nast, strongly, but before Vierge essentially opened up the Golden Age in France during the early Art Nouveau period Daumier was the most awesome illustrator out there.