I love the JC Bourne drawings (London and Birmingham Railway and Great Western Railway), the French impressionists, the railway poster art of the 20th century, and Turner's Rain, Steam, and Speed for starters. Some of the modern painters are excellent - I like Phillip Hawkins particularly, perhaps being a fellow Brummie helps. He does grime and the tough working conditions very well.
I can almost taste and feel the smoke in Monet's St. Lazare paintings.
My son is putting the best modern railway art to good purpose in his modelling by borrowing their designs for scenes on his layout.
RJD