One artist who's illustrations always claim my attention immediately are the works of Jon Klassen. Simple, witty, with tons of texture and color, all I can do is sit and ponder at what his process must be like. His illustrations are what my dreams are made of, I swear. If you only have time to check out one of his books, my absolute favorite is I Want My Hat Back.
Extra Yarn page 18 (Tree Sweater), Illustration by Jon Klassen