There are a number of books in the MCPL collection illustrated by Arthur Rackham. One of the most popular is The Wind in the Willows by Kenneth Grahame.
The illustrations done by John Tenniel for Lewis Carroll's Alice in Wonderland and Through the Looking Glass continue to spread their influence around the globe. You can see the echos of Tenniel in the sets, costumes, and characters of a number of movies.
There are vast varieties and styles of illustration. During the time of the of the LP record, album art was a critical part of the concept and marketing of music. Working out the story and iconography of the album cover art was sometimes an important aspect of appreciating the content. You can view a selection of album cover art in the Album Cover Album introduced by Dominy Hamilton and edited by Storm Thorgerson and Roger Dean.
Illustration is used currently and historically to sell products, to entice people into theatrical productions and various places of entertainment and to illustrate and spread political ideas. You can see all of these functions at work in the collection The Poster in History by Max Gallo with essays by Carlo Arturo Quintavalle and Charles Flowers. Posters provide enormous insight as to the styles, tastes, preferences, and viewpoints of people from all the times and places where the posters originate.
These selections barely skim the surface, and there is lots more to be found in MCPL. Look around in the children's picture books, in the illustrated DIY books, in photography, art, and almost every subject you will find good (and sometimes bad) examples of the illustrator's art.