Three birthdays that I didn't know about last year, so these need to be added to the list with Judith Kerr and Laurence Yep. I know American author, Janice May Udry only because of A Tree is Nice and I must say I think of Marc Simont before I think of her, but nevertheless she needs to be remembered as this book is definitely a classic. It was her first book and it won the Caldecott Medal in 1957!
Bruce Degen is much more prolific and thus well-known, as he the illustrator of Joanna Cole's Magic School Bus series as well as many other books such as Jamberry. You can watch him on a Reading Rockets video.
And thirdly, another American illustrator, Tom Lichtenheld who has become popular in my library recently because of Duck! Rabbit! (written by Amy Krouse Rosenthal), Shark vs Train (written by Chris Barton) and Goodnight, Goodnight, Construction Site (written by Sherri Duskey Rinker).