Over the years, great illustrators have created and shaped the popular vision of Santa Claus. Clockwise from top, left:
J. C. Leyendecker, who really created the modern vision of Santa [correction, see addendum below], and painted a number of memorable Saturday Evening Post covers featuring the jolly elf over the years. You can find them in the SEP cover archive.
Norman Rockwell, along with Leyendecker, provided numerous SEP covers with images of Santa, often with clever takes on the vision of his traditional role. The SEP cover archive has a section devoted to Rockwell Christmas covers.
Haddon Sundblom was an American illustrator who became noted for his yearly portrayals of Santa Claus for the Coca-Cola company. There is a section on the Coca-Cola site, and an album of Sundblom Santas here.
Addendum: I stand corrected. Stephen Worth of the ASIFA-Hollywood Animation Archive was kind enough to share with us illustrations from 1906 St. Nicholas Illustrated Magazine that show that illustrator Reginald Birch was in fact the one to flesh out Nast’s Civil War St. Nicholas concept into the the red-suited version we know today, prior to Leyendecker.
The Archive has posted a number of wonderful Birch illustrations from St. Nicholas Illustrated Magazine.
(Any fans of classic illustration and animation who are not familiar with ASIFA-Hollywood Animation Archive should click over there immediately and prepare to be amazed and delighted.)