What kind of stories does your boy like? Long attention span with lots of words per page, or a more active-style book with a lot of humor?
For more active books with less words per page, my kid loves anything by Mo Willems, especially Leonardo the Terrible Monster but also all of the Elephant and Piggie books and the Pigeon books. Richard Scarry is also a big hit around here - we have a couple of compilations (the Favorite Storybook Ever is the one we like best). We also like everything by Maurice Sendak, and anything with a good rhythm, like I Ain't Gonna Paint No More (Karen Beaumont), Tingo Tango Mango Tree, etc.
For longer reads, these are some favorites:
Amos & Boris, William Steig
All of the Henry & Mudge books by Cynthia Rylant
All of the Dr. Seuss brand educational books (Oh Say Can you Seed, Is A Camel a Mammal, etc)
Once Upon a Starry Night, Jacqueline Milton
Anything by Robert Munsch
Everything by Arnold Lobel
How I Became a Pirate, Melinda Long
Verdi, Janell Cannon
The Rainbow Goblins, Ul de Rico (this one is pretty dark but gorgeously illustrated)
We're also doing a lot of reading Aesop's Fables and books of myths and legends right now (my kid just turned 4, but we started them around 3.5).