Anything by Todd Parr are favourites here (bright pictures with simple yet impacting messages), and he loves looking at the pictures of The Eleventh Hour (by Graeme Base). One of my favourites is "And tango makes three", about two male penguins who fall in love and raise a chick together
We also love Little Green Books (his faves are "What do you see"? about endangered animals and "My first garden", about planting a garden at home).
Also, "Guess how much I love you" & "Love you forever", "Brown bear, brown bear, what do you see", "Dear Zoo", "Something from nothing" and "The very hungry caterpillar".
I can't wait to start reading the Faraway tree series with him by Enid Blyton, but he doesn't quite have the attention span for those ones yet.