Shaun Tan is one of Australia's most successful picturebook artists and authors. His work appears in books by Gary Crew (Memorial), John Marsden (The Rabbits), and others. His new book Rules of Summer (Available May 1) details the experiences of two friends who seem to break all the rules of summer (funny rules like don't step on a snail) intentionally and unintentionally. The interesting things that happen after the rules are broken is where the fun begins.
I also recommend The Lost Thing and The Red Tree. Shaun's website is filled with images and his writings about picturebooks and creativity: