Melissa Sweet has been illustrating children's books since 1990 when Pinky and Rex by James Howe was published. Since then, she has illustrated over 60 children's titles in her signature style of whimsical watercolors embelished with collage. In 2009, her illustrations for River of Words: The Story of William Carlos Williams received a Caldecott Honor citation.
You can read more about Melissa and see some of her art on her website. You can also find the transcript of an interview she gave about her artistic style and her creative process at the Eerdman's Books for Young Readers site. And of course, you can find her books through the library catalog.