Bud Plant is the biggest supplier of books by illustrators on the web, and they also have an excellent section of profiles on famous illustrators going as far back as the 19th century. Some of these profiles are also about famous comic strips (Bud Plant is mostly a comic site, but there are tons of illustrations materials there also), and famous people like Betty Page, the top pinup girl. I always find it fascinating to read these little bios about famous artists, you can often find little hints about what made them tick, and how they became successful.